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Theaetetus by Plato

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This etext was prepared by Sue Asscher


by Plato

Translated by Benjamin Jowett


Some dialogues of Plato are of so various a character that their relation
to the other dialogues cannot be determined with any degree of certainty.
The Theaetetus, like the Parmenides, has points of similarity both with his
earlier and his later writings. The perfection of style, the humour, the
dramatic interest, the complexity of structure, the fertility of
illustration, the shifting of the points of view, are characteristic of his
best period of authorship. The vain search, the negative conclusion, the
figure of the midwives, the constant profession of ignorance on the part of
Socrates, also bear the stamp of the early dialogues, in which the original
Socrates is not yet Platonized. Had we no other indications, we should be
disposed to range the Theaetetus with the Apology and the Phaedrus, and
perhaps even with the Protagoras and the Laches.

But when we pass from the style to an examination of the subject, we trace
a connection with the later rather than with the earlier dialogues. In the
first place there is the connexion, indicated by Plato himself at the end
of the dialogue, with the Sophist, to which in many respects the Theaetetus
is so little akin. (1) The same persons reappear, including the younger
Socrates, whose name is just mentioned in the Theaetetus; (2) the theory of
rest, which Socrates has declined to consider, is resumed by the Eleatic
Stranger; (3) there is a similar allusion in both dialogues to the meeting
of Parmenides and Socrates (Theaet., Soph.); and (4) the inquiry into not-
being in the Sophist supplements the question of false opinion which is
raised in the Theaetetus. (Compare also Theaet. and Soph. for parallel
turns of thought.) Secondly, the later date of the dialogue is confirmed
by the absence of the doctrine of recollection and of any doctrine of ideas
except that which derives them from generalization and from reflection of
the mind upon itself. The general character of the Theaetetus is
dialectical, and there are traces of the same Megarian influences which
appear in the Parmenides, and which later writers, in their matter of fact
way, have explained by the residence of Plato at Megara. Socrates
disclaims the character of a professional eristic, and also, with a sort of
ironical admiration, expresses his inability to attain the Megarian
precision in the use of terms. Yet he too employs a similar sophistical
skill in overturning every conceivable theory of knowledge.

The direct indications of a date amount to no more than this: the
conversation is said to have taken place when Theaetetus was a youth, and
shortly before the death of Socrates. At the time of his own death he is
supposed to be a full-grown man. Allowing nine or ten years for the
interval between youth and manhood, the dialogue could not have been
written earlier than 390, when Plato was about thirty-nine years of age.
No more definite date is indicated by the engagement in which Theaetetus is
said to have fallen or to have been wounded, and which may have taken place
any time during the Corinthian war, between the years 390-387. The later
date which has been suggested, 369, when the Athenians and Lacedaemonians
disputed the Isthmus with Epaminondas, would make the age of Theaetetus at
his death forty-five or forty-six. This a little impairs the beauty of
Socrates' remark, that 'he would be a great man if he lived.'

In this uncertainty about the place of the Theaetetus, it seemed better, as
in the case of the Republic, Timaeus, Critias, to retain the order in which
Plato himself has arranged this and the two companion dialogues. We cannot
exclude the possibility which has been already noticed in reference to
other works of Plato, that the Theaetetus may not have been all written
continuously; or the probability that the Sophist and Politicus, which
differ greatly in style, were only appended after a long interval of time.
The allusion to Parmenides compared with the Sophist, would probably imply
that the dialogue which is called by his name was already in existence;
unless, indeed, we suppose the passage in which the allusion occurs to have
been inserted afterwards. Again, the Theaetetus may be connected with the
Gorgias, either dialogue from different points of view containing an
analysis of the real and apparent (Schleiermacher); and both may be brought
into relation with the Apology as illustrating the personal life of
Socrates. The Philebus, too, may with equal reason be placed either after
or before what, in the language of Thrasyllus, may be called the Second
Platonic Trilogy. Both the Parmenides and the Sophist, and still more the
Theaetetus, have points of affinity with the Cratylus, in which the
principles of rest and motion are again contrasted, and the Sophistical or
Protagorean theory of language is opposed to that which is attributed to
the disciple of Heracleitus, not to speak of lesser resemblances in thought
and language. The Parmenides, again, has been thought by some to hold an
intermediate position between the Theaetetus and the Sophist; upon this
view, the Sophist may be regarded as the answer to the problems about One
and Being which have been raised in the Parmenides. Any of these
arrangements may suggest new views to the student of Plato; none of them
can lay claim to an exclusive probability in its favour.

The Theaetetus is one of the narrated dialogues of Plato, and is the only
one which is supposed to have been written down. In a short introductory
scene, Euclides and Terpsion are described as meeting before the door of
Euclides' house in Megara. This may have been a spot familiar to Plato
(for Megara was within a walk of Athens), but no importance can be attached
to the accidental introduction of the founder of the Megarian philosophy.
The real intention of the preface is to create an interest about the person
of Theaetetus, who has just been carried up from the army at Corinth in a
dying state. The expectation of his death recalls the promise of his
youth, and especially the famous conversation which Socrates had with him
when he was quite young, a few days before his own trial and death, as we
are once more reminded at the end of the dialogue. Yet we may observe that
Plato has himself forgotten this, when he represents Euclides as from time
to time coming to Athens and correcting the copy from Socrates' own mouth.
The narrative, having introduced Theaetetus, and having guaranteed the
authenticity of the dialogue (compare Symposium, Phaedo, Parmenides), is
then dropped. No further use is made of the device. As Plato himself
remarks, who in this as in some other minute points is imitated by Cicero
(De Amicitia), the interlocutory words are omitted.

Theaetetus, the hero of the battle of Corinth and of the dialogue, is a
disciple of Theodorus, the great geometrician, whose science is thus
indicated to be the propaedeutic to philosophy. An interest has been
already excited about him by his approaching death, and now he is
introduced to us anew by the praises of his master Theodorus. He is a
youthful Socrates, and exhibits the same contrast of the fair soul and the
ungainly face and frame, the Silenus mask and the god within, which are
described in the Symposium. The picture which Theodorus gives of his
courage and patience and intelligence and modesty is verified in the course
of the dialogue. His courage is shown by his behaviour in the battle, and
his other qualities shine forth as the argument proceeds. Socrates takes
an evident delight in 'the wise Theaetetus,' who has more in him than 'many
bearded men'; he is quite inspired by his answers. At first the youth is
lost in wonder, and is almost too modest to speak, but, encouraged by
Socrates, he rises to the occasion, and grows full of interest and
enthusiasm about the great question. Like a youth, he has not finally made
up his mind, and is very ready to follow the lead of Socrates, and to enter
into each successive phase of the discussion which turns up. His great
dialectical talent is shown in his power of drawing distinctions, and of
foreseeing the consequences of his own answers. The enquiry about the
nature of knowledge is not new to him; long ago he has felt the 'pang of
philosophy,' and has experienced the youthful intoxication which is
depicted in the Philebus. But he has hitherto been unable to make the
transition from mathematics to metaphysics. He can form a general
conception of square and oblong numbers, but he is unable to attain a
similar expression of knowledge in the abstract. Yet at length he begins
to recognize that there are universal conceptions of being, likeness,
sameness, number, which the mind contemplates in herself, and with the help
of Socrates is conducted from a theory of sense to a theory of ideas.

There is no reason to doubt that Theaetetus was a real person, whose name
survived in the next generation. But neither can any importance be
attached to the notices of him in Suidas and Proclus, which are probably
based on the mention of him in Plato. According to a confused statement in
Suidas, who mentions him twice over, first, as a pupil of Socrates, and
then of Plato, he is said to have written the first work on the Five
Solids. But no early authority cites the work, the invention of which may
have been easily suggested by the division of roots, which Plato attributes
to him, and the allusion to the backward state of solid geometry in the
Republic. At any rate, there is no occasion to recall him to life again
after the battle of Corinth, in order that we may allow time for the
completion of such a work (Muller). We may also remark that such a
supposition entirely destroys the pathetic interest of the introduction.

Theodorus, the geometrician, had once been the friend and disciple of
Protagoras, but he is very reluctant to leave his retirement and defend his
old master. He is too old to learn Socrates' game of question and answer,
and prefers the digressions to the main argument, because he finds them
easier to follow. The mathematician, as Socrates says in the Republic, is
not capable of giving a reason in the same manner as the dialectician, and
Theodorus could not therefore have been appropriately introduced as the
chief respondent. But he may be fairly appealed to, when the honour of his
master is at stake. He is the 'guardian of his orphans,' although this is
a responsibility which he wishes to throw upon Callias, the friend and
patron of all Sophists, declaring that he himself had early 'run away' from
philosophy, and was absorbed in mathematics. His extreme dislike to the
Heraclitean fanatics, which may be compared with the dislike of Theaetetus
to the materialists, and his ready acceptance of the noble words of
Socrates, are noticeable traits of character.

The Socrates of the Theaetetus is the same as the Socrates of the earlier
dialogues. He is the invincible disputant, now advanced in years, of the
Protagoras and Symposium; he is still pursuing his divine mission, his
'Herculean labours,' of which he has described the origin in the Apology;
and he still hears the voice of his oracle, bidding him receive or not
receive the truant souls. There he is supposed to have a mission to
convict men of self-conceit; in the Theaetetus he has assigned to him by
God the functions of a man-midwife, who delivers men of their thoughts, and
under this character he is present throughout the dialogue. He is the true
prophet who has an insight into the natures of men, and can divine their
future; and he knows that sympathy is the secret power which unlocks their
thoughts. The hit at Aristides, the son of Lysimachus, who was specially
committed to his charge in the Laches, may be remarked by the way. The
attempt to discover the definition of knowledge is in accordance with the
character of Socrates as he is described in the Memorabilia, asking What is
justice? what is temperance? and the like. But there is no reason to
suppose that he would have analyzed the nature of perception, or traced the
connexion of Protagoras and Heracleitus, or have raised the difficulty
respecting false opinion. The humorous illustrations, as well as the
serious thoughts, run through the dialogue. The snubnosedness of
Theaetetus, a characteristic which he shares with Socrates, and the man-
midwifery of Socrates, are not forgotten in the closing words. At the end
of the dialogue, as in the Euthyphro, he is expecting to meet Meletus at
the porch of the king Archon; but with the same indifference to the result
which is everywhere displayed by him, he proposes that they shall
reassemble on the following day at the same spot. The day comes, and in
the Sophist the three friends again meet, but no further allusion is made
to the trial, and the principal share in the argument is assigned, not to
Socrates, but to an Eleatic stranger; the youthful Theaetetus also plays a
different and less independent part. And there is no allusion in the
Introduction to the second and third dialogues, which are afterwards
appended. There seems, therefore, reason to think that there is a real
change, both in the characters and in the design.

The dialogue is an enquiry into the nature of knowledge, which is
interrupted by two digressions. The first is the digression about the
midwives, which is also a leading thought or continuous image, like the
wave in the Republic, appearing and reappearing at intervals. Again and
again we are reminded that the successive conceptions of knowledge are
extracted from Theaetetus, who in his turn truly declares that Socrates has
got a great deal more out of him than ever was in him. Socrates is never
weary of working out the image in humorous details,--discerning the
symptoms of labour, carrying the child round the hearth, fearing that
Theaetetus will bite him, comparing his conceptions to wind-eggs, asserting
an hereditary right to the occupation. There is also a serious side to the
image, which is an apt similitude of the Socratic theory of education
(compare Republic, Sophist), and accords with the ironical spirit in which
the wisest of men delights to speak of himself.

The other digression is the famous contrast of the lawyer and philosopher.
This is a sort of landing-place or break in the middle of the dialogue. At
the commencement of a great discussion, the reflection naturally arises,
How happy are they who, like the philosopher, have time for such
discussions (compare Republic)! There is no reason for the introduction of
such a digression; nor is a reason always needed, any more than for the
introduction of an episode in a poem, or of a topic in conversation. That
which is given by Socrates is quite sufficient, viz. that the philosopher
may talk and write as he pleases. But though not very closely connected,
neither is the digression out of keeping with the rest of the dialogue.
The philosopher naturally desires to pour forth the thoughts which are
always present to him, and to discourse of the higher life. The idea of
knowledge, although hard to be defined, is realised in the life of
philosophy. And the contrast is the favourite antithesis between the
world, in the various characters of sophist, lawyer, statesman, speaker,
and the philosopher,--between opinion and knowledge,--between the
conventional and the true.

The greater part of the dialogue is devoted to setting up and throwing down
definitions of science and knowledge. Proceeding from the lower to the
higher by three stages, in which perception, opinion, reasoning are
successively examined, we first get rid of the confusion of the idea of
knowledge and specific kinds of knowledge,--a confusion which has been
already noticed in the Lysis, Laches, Meno, and other dialogues. In the
infancy of logic, a form of thought has to be invented before the content
can be filled up. We cannot define knowledge until the nature of
definition has been ascertained. Having succeeded in making his meaning
plain, Socrates proceeds to analyze (1) the first definition which
Theaetetus proposes: 'Knowledge is sensible perception.' This is speedily
identified with the Protagorean saying, 'Man is the measure of all things;'
and of this again the foundation is discovered in the perpetual flux of
Heracleitus. The relativeness of sensation is then developed at length,
and for a moment the definition appears to be accepted. But soon the
Protagorean thesis is pronounced to be suicidal; for the adversaries of
Protagoras are as good a measure as he is, and they deny his doctrine. He
is then supposed to reply that the perception may be true at any given
instant. But the reply is in the end shown to be inconsistent with the
Heraclitean foundation, on which the doctrine has been affirmed to rest.
For if the Heraclitean flux is extended to every sort of change in every
instant of time, how can any thought or word be detained even for an
instant? Sensible perception, like everything else, is tumbling to pieces.
Nor can Protagoras himself maintain that one man is as good as another in
his knowledge of the future; and 'the expedient,' if not 'the just and
true,' belongs to the sphere of the future.

And so we must ask again, What is knowledge? The comparison of sensations
with one another implies a principle which is above sensation, and which
resides in the mind itself. We are thus led to look for knowledge in a
higher sphere, and accordingly Theaetetus, when again interrogated, replies
(2) that 'knowledge is true opinion.' But how is false opinion possible?
The Megarian or Eristic spirit within us revives the question, which has
been already asked and indirectly answered in the Meno: 'How can a man be
ignorant of that which he knows?' No answer is given to this not
unanswerable question. The comparison of the mind to a block of wax, or to
a decoy of birds, is found wanting.

But are we not inverting the natural order in looking for opinion before we
have found knowledge? And knowledge is not true opinion; for the Athenian
dicasts have true opinion but not knowledge. What then is knowledge? We
answer (3), 'True opinion, with definition or explanation.' But all the
different ways in which this statement may be understood are set aside,
like the definitions of courage in the Laches, or of friendship in the
Lysis, or of temperance in the Charmides. At length we arrive at the
conclusion, in which nothing is concluded.

There are two special difficulties which beset the student of the
Theaetetus: (1) he is uncertain how far he can trust Plato's account of
the theory of Protagoras; and he is also uncertain (2) how far, and in what
parts of the dialogue, Plato is expressing his own opinion. The dramatic
character of the work renders the answer to both these questions difficult.

1. In reply to the first, we have only probabilities to offer. Three main
points have to be decided: (a) Would Protagoras have identified his own
thesis, 'Man is the measure of all things,' with the other, 'All knowledge
is sensible perception'? (b) Would he have based the relativity of
knowledge on the Heraclitean flux? (c) Would he have asserted the
absoluteness of sensation at each instant? Of the work of Protagoras on
'Truth' we know nothing, with the exception of the two famous fragments,
which are cited in this dialogue, 'Man is the measure of all things,' and,
'Whether there are gods or not, I cannot tell.' Nor have we any other
trustworthy evidence of the tenets of Protagoras, or of the sense in which
his words are used. For later writers, including Aristotle in his
Metaphysics, have mixed up the Protagoras of Plato, as they have the
Socrates of Plato, with the real person.

Returning then to the Theaetetus, as the only possible source from which an
answer to these questions can be obtained, we may remark, that Plato had
'The Truth' of Protagoras before him, and frequently refers to the book.
He seems to say expressly, that in this work the doctrine of the
Heraclitean flux was not to be found; 'he told the real truth' (not in the
book, which is so entitled, but) 'privately to his disciples,'--words which
imply that the connexion between the doctrines of Protagoras and
Heracleitus was not generally recognized in Greece, but was really
discovered or invented by Plato. On the other hand, the doctrine that 'Man
is the measure of all things,' is expressly identified by Socrates with the
other statement, that 'What appears to each man is to him;' and a reference
is made to the books in which the statement occurs;--this Theaetetus, who
has 'often read the books,' is supposed to acknowledge (so Cratylus). And
Protagoras, in the speech attributed to him, never says that he has been
misunderstood: he rather seems to imply that the absoluteness of sensation
at each instant was to be found in his words. He is only indignant at the
'reductio ad absurdum' devised by Socrates for his 'homo mensura,' which
Theodorus also considers to be 'really too bad.'

The question may be raised, how far Plato in the Theaetetus could have
misrepresented Protagoras without violating the laws of dramatic
probability. Could he have pretended to cite from a well-known writing
what was not to be found there? But such a shadowy enquiry is not worth
pursuing further. We need only remember that in the criticism which
follows of the thesis of Protagoras, we are criticizing the Protagoras of
Plato, and not attempting to draw a precise line between his real
sentiments and those which Plato has attributed to him.

2. The other difficulty is a more subtle, and also a more important one,
because bearing on the general character of the Platonic dialogues. On a
first reading of them, we are apt to imagine that the truth is only spoken
by Socrates, who is never guilty of a fallacy himself, and is the great
detector of the errors and fallacies of others. But this natural
presumption is disturbed by the discovery that the Sophists are sometimes
in the right and Socrates in the wrong. Like the hero of a novel, he is
not to be supposed always to represent the sentiments of the author. There
are few modern readers who do not side with Protagoras, rather than with
Socrates, in the dialogue which is called by his name. The Cratylus
presents a similar difficulty: in his etymologies, as in the number of the
State, we cannot tell how far Socrates is serious; for the Socratic irony
will not allow him to distinguish between his real and his assumed wisdom.
No one is the superior of the invincible Socrates in argument (except in
the first part of the Parmenides, where he is introduced as a youth); but
he is by no means supposed to be in possession of the whole truth.
Arguments are often put into his mouth (compare Introduction to the
Gorgias) which must have seemed quite as untenable to Plato as to a modern
writer. In this dialogue a great part of the answer of Protagoras is just
and sound; remarks are made by him on verbal criticism, and on the
importance of understanding an opponent's meaning, which are conceived in
the true spirit of philosophy. And the distinction which he is supposed to
draw between Eristic and Dialectic, is really a criticism of Plato on
himself and his own criticism of Protagoras.

The difficulty seems to arise from not attending to the dramatic character
of the writings of Plato. There are two, or more, sides to questions; and
these are parted among the different speakers. Sometimes one view or
aspect of a question is made to predominate over the rest, as in the
Gorgias or Sophist; but in other dialogues truth is divided, as in the
Laches and Protagoras, and the interest of the piece consists in the
contrast of opinions. The confusion caused by the irony of Socrates, who,
if he is true to his character, cannot say anything of his own knowledge,
is increased by the circumstance that in the Theaetetus and some other
dialogues he is occasionally playing both parts himself, and even charging
his own arguments with unfairness. In the Theaetetus he is designedly held
back from arriving at a conclusion. For we cannot suppose that Plato
conceived a definition of knowledge to be impossible. But this is his
manner of approaching and surrounding a question. The lights which he
throws on his subject are indirect, but they are not the less real for
that. He has no intention of proving a thesis by a cut-and-dried argument;
nor does he imagine that a great philosophical problem can be tied up
within the limits of a definition. If he has analyzed a proposition or
notion, even with the severity of an impossible logic, if half-truths have
been compared by him with other half-truths, if he has cleared up or
advanced popular ideas, or illustrated a new method, his aim has been
sufficiently accomplished.

The writings of Plato belong to an age in which the power of analysis had
outrun the means of knowledge; and through a spurious use of dialectic, the
distinctions which had been already 'won from the void and formless
infinite,' seemed to be rapidly returning to their original chaos. The two
great speculative philosophies, which a century earlier had so deeply
impressed the mind of Hellas, were now degenerating into Eristic. The
contemporaries of Plato and Socrates were vainly trying to find new
combinations of them, or to transfer them from the object to the subject.
The Megarians, in their first attempts to attain a severer logic, were
making knowledge impossible (compare Theaet.). They were asserting 'the
one good under many names,' and, like the Cynics, seem to have denied
predication, while the Cynics themselves were depriving virtue of all which
made virtue desirable in the eyes of Socrates and Plato. And besides
these, we find mention in the later writings of Plato, especially in the
Theaetetus, Sophist, and Laws, of certain impenetrable godless persons, who
will not believe what they 'cannot hold in their hands'; and cannot be
approached in argument, because they cannot argue (Theat; Soph.). No
school of Greek philosophers exactly answers to these persons, in whom
Plato may perhaps have blended some features of the Atomists with the
vulgar materialistic tendencies of mankind in general (compare Introduction
to the Sophist).

And not only was there a conflict of opinions, but the stage which the mind
had reached presented other difficulties hardly intelligible to us, who
live in a different cycle of human thought. All times of mental progress
are times of confusion; we only see, or rather seem to see things clearly,
when they have been long fixed and defined. In the age of Plato, the
limits of the world of imagination and of pure abstraction, of the old
world and the new, were not yet fixed. The Greeks, in the fourth century
before Christ, had no words for 'subject' and 'object,' and no distinct
conception of them; yet they were always hovering about the question
involved in them. The analysis of sense, and the analysis of thought, were
equally difficult to them; and hopelessly confused by the attempt to solve
them, not through an appeal to facts, but by the help of general theories
respecting the nature of the universe.

Plato, in his Theaetetus, gathers up the sceptical tendencies of his age,
and compares them. But he does not seek to reconstruct out of them a
theory of knowledge. The time at which such a theory could be framed had
not yet arrived. For there was no measure of experience with which the
ideas swarming in men's minds could be compared; the meaning of the word
'science' could scarcely be explained to them, except from the mathematical
sciences, which alone offered the type of universality and certainty.
Philosophy was becoming more and more vacant and abstract, and not only the
Platonic Ideas and the Eleatic Being, but all abstractions seemed to be at
variance with sense and at war with one another.

The want of the Greek mind in the fourth century before Christ was not
another theory of rest or motion, or Being or atoms, but rather a
philosophy which could free the mind from the power of abstractions and
alternatives, and show how far rest and how far motion, how far the
universal principle of Being and the multitudinous principle of atoms,
entered into the composition of the world; which could distinguish between
the true and false analogy, and allow the negative as well as the positive
a place in human thought. To such a philosophy Plato, in the Theaetetus,
offers many contributions. He has followed philosophy into the region of
mythology, and pointed out the similarities of opposing phases of thought.
He has also shown that extreme abstractions are self-destructive, and,
indeed, hardly distinguishable from one another. But his intention is not
to unravel the whole subject of knowledge, if this had been possible; and
several times in the course of the dialogue he rejects explanations of
knowledge which have germs of truth in them; as, for example, 'the
resolution of the compound into the simple;' or 'right opinion with a mark
of difference.'


Terpsion, who has come to Megara from the country, is described as having
looked in vain for Euclides in the Agora; the latter explains that he has
been down to the harbour, and on his way thither had met Theaetetus, who
was being carried up from the army to Athens. He was scarcely alive, for
he had been badly wounded at the battle of Corinth, and had taken the
dysentery which prevailed in the camp. The mention of his condition
suggests the reflection, 'What a loss he will be!' 'Yes, indeed,' replies
Euclid; 'only just now I was hearing of his noble conduct in the battle.'
'That I should expect; but why did he not remain at Megara?' 'I wanted him
to remain, but he would not; so I went with him as far as Erineum; and as I
parted from him, I remembered that Socrates had seen him when he was a
youth, and had a remarkable conversation with him, not long before his own
death; and he then prophesied of him that he would be a great man if he
lived.' 'How true that has been; how like all that Socrates said! And
could you repeat the conversation?' 'Not from memory; but I took notes
when I returned home, which I afterwards filled up at leisure, and got
Socrates to correct them from time to time, when I came to
Athens'...Terpsion had long intended to ask for a sight of this writing, of
which he had already heard. They are both tired, and agree to rest and
have the conversation read to them by a servant...'Here is the roll,
Terpsion; I need only observe that I have omitted, for the sake of
convenience, the interlocutory words, "said I," "said he"; and that
Theaetetus, and Theodorus, the geometrician of Cyrene, are the persons with
whom Socrates is conversing.'

Socrates begins by asking Theodorus whether, in his visit to Athens, he has
found any Athenian youth likely to attain distinction in science. 'Yes,
Socrates, there is one very remarkable youth, with whom I have become
acquainted. He is no beauty, and therefore you need not imagine that I am
in love with him; and, to say the truth, he is very like you, for he has a
snub nose, and projecting eyes, although these features are not so marked
in him as in you. He combines the most various qualities, quickness,
patience, courage; and he is gentle as well as wise, always silently
flowing on, like a river of oil. Look! he is the middle one of those who
are entering the palaestra.'

Socrates, who does not know his name, recognizes him as the son of
Euphronius, who was himself a good man and a rich. He is informed by
Theodorus that the youth is named Theaetetus, but the property of his
father has disappeared in the hands of trustees; this does not, however,
prevent him from adding liberality to his other virtues. At the desire of
Socrates he invites Theaetetus to sit by them.

'Yes,' says Socrates, 'that I may see in you, Theaetetus, the image of my
ugly self, as Theodorus declares. Not that his remark is of any
importance; for though he is a philosopher, he is not a painter, and
therefore he is no judge of our faces; but, as he is a man of science, he
may be a judge of our intellects. And if he were to praise the mental
endowments of either of us, in that case the hearer of the eulogy ought to
examine into what he says, and the subject should not refuse to be
examined.' Theaetetus consents, and is caught in a trap (compare the
similar trap which is laid for Theodorus). 'Then, Theaetetus, you will
have to be examined, for Theodorus has been praising you in a style of
which I never heard the like.' 'He was only jesting.' 'Nay, that is not
his way; and I cannot allow you, on that pretence, to retract the assent
which you have already given, or I shall make Theodorus repeat your
praises, and swear to them.' Theaetetus, in reply, professes that he is
willing to be examined, and Socrates begins by asking him what he learns of
Theodorus. He is himself anxious to learn anything of anybody; and now he
has a little question to which he wants Theaetetus or Theodorus (or
whichever of the company would not be 'donkey' to the rest) to find an
answer. Without further preface, but at the same time apologizing for his
eagerness, he asks, 'What is knowledge?' Theodorus is too old to answer
questions, and begs him to interrogate Theaetetus, who has the advantage of

Theaetetus replies, that knowledge is what he learns of Theodorus, i.e.
geometry and arithmetic; and that there are other kinds of knowledge--
shoemaking, carpentering, and the like. But Socrates rejoins, that this
answer contains too much and also too little. For although Theaetetus has
enumerated several kinds of knowledge, he has not explained the common
nature of them; as if he had been asked, 'What is clay?' and instead of
saying 'Clay is moistened earth,' he had answered, 'There is one clay of
image-makers, another of potters, another of oven-makers.' Theaetetus at
once divines that Socrates means him to extend to all kinds of knowledge
the same process of generalization which he has already learned to apply to
arithmetic. For he has discovered a division of numbers into square
numbers, 4, 9, 16, etc., which are composed of equal factors, and represent
figures which have equal sides, and oblong numbers, 3, 5, 6, 7, etc., which
are composed of unequal factors, and represent figures which have unequal
sides. But he has never succeeded in attaining a similar conception of
knowledge, though he has often tried; and, when this and similar questions
were brought to him from Socrates, has been sorely distressed by them.
Socrates explains to him that he is in labour. For men as well as women
have pangs of labour; and both at times require the assistance of midwives.
And he, Socrates, is a midwife, although this is a secret; he has inherited
the art from his mother bold and bluff, and he ushers into light, not
children, but the thoughts of men. Like the midwives, who are 'past
bearing children,' he too can have no offspring--the God will not allow him
to bring anything into the world of his own. He also reminds Theaetetus
that the midwives are or ought to be the only matchmakers (this is the
preparation for a biting jest); for those who reap the fruit are most
likely to know on what soil the plants will grow. But respectable midwives
avoid this department of practice--they do not want to be called
procuresses. There are some other differences between the two sorts of
pregnancy. For women do not bring into the world at one time real children
and at another time idols which are with difficulty distinguished from
them. 'At first,' says Socrates in his character of the man-midwife, 'my
patients are barren and stolid, but after a while they "round apace," if
the gods are propitious to them; and this is due not to me but to
themselves; I and the god only assist in bringing their ideas to the birth.
Many of them have left me too soon, and the result has been that they have
produced abortions; or when I have delivered them of children they have
lost them by an ill bringing up, and have ended by seeing themselves, as
others see them, to be great fools. Aristides, the son of Lysimachus, is
one of these, and there have been others. The truants often return to me
and beg to be taken back; and then, if my familiar allows me, which is not
always the case, I receive them, and they begin to grow again. There come
to me also those who have nothing in them, and have no need of my art; and
I am their matchmaker (see above), and marry them to Prodicus or some other
inspired sage who is likely to suit them. I tell you this long story
because I suspect that you are in labour. Come then to me, who am a
midwife, and the son of a midwife, and I will deliver you. And do not bite
me, as the women do, if I abstract your first-born; for I am acting out of
good-will towards you; the God who is within me is the friend of man,
though he will not allow me to dissemble the truth. Once more then,
Theaetetus, I repeat my old question--"What is knowledge?" Take courage,
and by the help of God you will discover an answer.' 'My answer is, that
knowledge is perception.' 'That is the theory of Protagoras, who has
another way of expressing the same thing when he says, "Man is the measure
of all things." He was a very wise man, and we should try to understand
him. In order to illustrate his meaning let me suppose that there is the
same wind blowing in our faces, and one of us may be hot and the other
cold. How is this? Protagoras will reply that the wind is hot to him who
is cold, cold to him who is hot. And "is" means "appears," and when you
say "appears to him," that means "he feels." Thus feeling, appearance,
perception, coincide with being. I suspect, however, that this was only a
"facon de parler," by which he imposed on the common herd like you and me;
he told "the truth" (in allusion to the title of his book, which was called
"The Truth") in secret to his disciples. For he was really a votary of
that famous philosophy in which all things are said to be relative; nothing
is great or small, or heavy or light, or one, but all is in motion and
mixture and transition and flux and generation, not "being," as we
ignorantly affirm, but "becoming." This has been the doctrine, not of
Protagoras only, but of all philosophers, with the single exception of
Parmenides; Empedocles, Heracleitus, and others, and all the poets, with
Epicharmus, the king of Comedy, and Homer, the king of Tragedy, at their
head, have said the same; the latter has these words--

"Ocean, whence the gods sprang, and mother Tethys."

And many arguments are used to show, that motion is the source of life, and
rest of death: fire and warmth are produced by friction, and living
creatures owe their origin to a similar cause; the bodily frame is
preserved by exercise and destroyed by indolence; and if the sun ceased to
move, "chaos would come again." Now apply this doctrine of "All is motion"
to the senses, and first of all to the sense of sight. The colour of
white, or any other colour, is neither in the eyes nor out of them, but
ever in motion between the object and the eye, and varying in the case of
every percipient. All is relative, and, as the followers of Protagoras
remark, endless contradictions arise when we deny this; e.g. here are six
dice; they are more than four and less than twelve; "more and also less,"
would you not say?' 'Yes.' 'But Protagoras will retort: "Can anything be
more or less without addition or subtraction?"'

'I should say "No" if I were not afraid of contradicting my former answer.'

'And if you say "Yes," the tongue will escape conviction but not the mind,
as Euripides would say?' 'True.' 'The thoroughbred Sophists, who know all
that can be known, would have a sparring match over this, but you and I,
who have no professional pride, want only to discover whether our ideas are
clear and consistent. And we cannot be wrong in saying, first, that
nothing can be greater or less while remaining equal; secondly, that there
can be no becoming greater or less without addition or subtraction;
thirdly, that what is and was not, cannot be without having become. But
then how is this reconcilable with the case of the dice, and with similar
examples?--that is the question.' 'I am often perplexed and amazed,
Socrates, by these difficulties.' 'That is because you are a philosopher,
for philosophy begins in wonder, and Iris is the child of Thaumas. Do you
know the original principle on which the doctrine of Protagoras is based?'
'No.' 'Then I will tell you; but we must not let the uninitiated hear, and
by the uninitiated I mean the obstinate people who believe in nothing which
they cannot hold in their hands. The brethren whose mysteries I am about
to unfold to you are far more ingenious. They maintain that all is motion;
and that motion has two forms, action and passion, out of which endless
phenomena are created, also in two forms--sense and the object of sense--
which come to the birth together. There are two kinds of motions, a slow
and a fast; the motions of the agent and the patient are slower, because
they move and create in and about themselves, but the things which are born
of them have a swifter motion, and pass rapidly from place to place. The
eye and the appropriate object come together, and give birth to whiteness
and the sensation of whiteness; the eye is filled with seeing, and becomes
not sight but a seeing eye, and the object is filled with whiteness, and
becomes not whiteness but white; and no other compound of either with
another would have produced the same effect. All sensation is to be
resolved into a similar combination of an agent and patient. Of either,
taken separately, no idea can be formed; and the agent may become a
patient, and the patient an agent. Hence there arises a general reflection
that nothing is, but all things become; no name can detain or fix them.
Are not these speculations charming, Theaetetus, and very good for a person
in your interesting situation? I am offering you specimens of other men's
wisdom, because I have no wisdom of my own, and I want to deliver you of
something; and presently we will see whether you have brought forth wind or
not. Tell me, then, what do you think of the notion that "All things are

'When I hear your arguments, I am marvellously ready to assent.'

'But I ought not to conceal from you that there is a serious objection
which may be urged against this doctrine of Protagoras. For there are
states, such as madness and dreaming, in which perception is false; and
half our life is spent in dreaming; and who can say that at this instant we
are not dreaming? Even the fancies of madmen are real at the time. But if
knowledge is perception, how can we distinguish between the true and the
false in such cases? Having stated the objection, I will now state the
answer. Protagoras would deny the continuity of phenomena; he would say
that what is different is entirely different, and whether active or passive
has a different power. There are infinite agents and patients in the
world, and these produce in every combination of them a different
perception. Take myself as an instance:--Socrates may be ill or he may be
well,--and remember that Socrates, with all his accidents, is spoken of.
The wine which I drink when I am well is pleasant to me, but the same wine
is unpleasant to me when I am ill. And there is nothing else from which I
can receive the same impression, nor can another receive the same
impression from the wine. Neither can I and the object of sense become
separately what we become together. For the one in becoming is relative to
the other, but they have no other relation; and the combination of them is
absolute at each moment. (In modern language, the act of sensation is
really indivisible, though capable of a mental analysis into subject and
object.) My sensation alone is true, and true to me only. And therefore,
as Protagoras says, "To myself I am the judge of what is and what is not."
Thus the flux of Homer and Heracleitus, the great Protagorean saying that
"Man is the measure of all things," the doctrine of Theaetetus that
"Knowledge is perception," have all the same meaning. And this is thy new-
born child, which by my art I have brought to light; and you must not be
angry if instead of rearing your infant we expose him.'

'Theaetetus will not be angry,' says Theodorus; 'he is very good-natured.
But I should like to know, Socrates, whether you mean to say that all this
is untrue?'

'First reminding you that I am not the bag which contains the arguments,
but that I extract them from Theaetetus, shall I tell you what amazes me in
your friend Protagoras?'

'What may that be?'

'I like his doctrine that what appears is; but I wonder that he did not
begin his great work on Truth with a declaration that a pig, or a dog-faced
baboon, or any other monster which has sensation, is a measure of all
things; then, while we were reverencing him as a god, he might have
produced a magnificent effect by expounding to us that he was no wiser than
a tadpole. For if sensations are always true, and one man's discernment is
as good as another's, and every man is his own judge, and everything that
he judges is right and true, then what need of Protagoras to be our
instructor at a high figure; and why should we be less knowing than he is,
or have to go to him, if every man is the measure of all things? My own
art of midwifery, and all dialectic, is an enormous folly, if Protagoras'
"Truth" be indeed truth, and the philosopher is not merely amusing himself
by giving oracles out of his book.'

Theodorus thinks that Socrates is unjust to his master, Protagoras; but he
is too old and stiff to try a fall with him, and therefore refers him to
Theaetetus, who is already driven out of his former opinion by the
arguments of Socrates.

Socrates then takes up the defence of Protagoras, who is supposed to reply
in his own person--'Good people, you sit and declaim about the gods, of
whose existence or non-existence I have nothing to say, or you discourse
about man being reduced to the level of the brutes; but what proof have you
of your statements? And yet surely you and Theodorus had better reflect
whether probability is a safe guide. Theodorus would be a bad geometrician
if he had nothing better to offer.'...Theaetetus is affected by the appeal
to geometry, and Socrates is induced by him to put the question in a new
form. He proceeds as follows:--'Should we say that we know what we see and
hear,--e.g. the sound of words or the sight of letters in a foreign

'We should say that the figures of the letters, and the pitch of the voice
in uttering them, were known to us, but not the meaning of them.'

'Excellent; I want you to grow, and therefore I will leave that answer and
ask another question: Is not seeing perceiving?' 'Very true.' 'And he
who sees knows?' 'Yes.' 'And he who remembers, remembers that which he
sees and knows?' 'Very true.' 'But if he closes his eyes, does he not
remember?' 'He does.' 'Then he may remember and not see; and if seeing is
knowing, he may remember and not know. Is not this a "reductio ad
absurdum" of the hypothesis that knowledge is sensible perception? Yet
perhaps we are crowing too soon; and if Protagoras, "the father of the
myth," had been alive, the result might have been very different. But he
is dead, and Theodorus, whom he left guardian of his "orphan," has not been
very zealous in defending him.'

Theodorus objects that Callias is the true guardian, but he hopes that
Socrates will come to the rescue. Socrates prefaces his defence by
resuming the attack. He asks whether a man can know and not know at the
same time? 'Impossible.' Quite possible, if you maintain that seeing is
knowing. The confident adversary, suiting the action to the word, shuts
one of your eyes; and now, says he, you see and do not see, but do you know
and not know? And a fresh opponent darts from his ambush, and transfers to
knowledge the terms which are commonly applied to sight. He asks whether
you can know near and not at a distance; whether you can have a sharp and
also a dull knowledge. While you are wondering at his incomparable wisdom,
he gets you into his power, and you will not escape until you have come to
an understanding with him about the money which is to be paid for your

But Protagoras has not yet made his defence; and already he may be heard
contemptuously replying that he is not responsible for the admissions which
were made by a boy, who could not foresee the coming move, and therefore
had answered in a manner which enabled Socrates to raise a laugh against
himself. 'But I cannot be fairly charged,' he will say, 'with an answer
which I should not have given; for I never maintained that the memory of a
feeling is the same as a feeling, or denied that a man might know and not
know the same thing at the same time. Or, if you will have extreme
precision, I say that man in different relations is many or rather infinite
in number. And I challenge you, either to show that his perceptions are
not individual, or that if they are, what appears to him is not what is.
As to your pigs and baboons, you are yourself a pig, and you make my
writings a sport of other swine. But I still affirm that man is the
measure of all things, although I admit that one man may be a thousand
times better than another, in proportion as he has better impressions.
Neither do I deny the existence of wisdom or of the wise man. But I
maintain that wisdom is a practical remedial power of turning evil into
good, the bitterness of disease into the sweetness of health, and does not
consist in any greater truth or superior knowledge. For the impressions of
the sick are as true as the impressions of the healthy; and the sick are as
wise as the healthy. Nor can any man be cured of a false opinion, for
there is no such thing; but he may be cured of the evil habit which
generates in him an evil opinion. This is effected in the body by the
drugs of the physician, and in the soul by the words of the Sophist; and
the new state or opinion is not truer, but only better than the old. And
philosophers are not tadpoles, but physicians and husbandmen, who till the
soil and infuse health into animals and plants, and make the good take the
place of the evil, both in individuals and states. Wise and good
rhetoricians make the good to appear just in states (for that is just which
appears just to a state), and in return, they deserve to be well paid. And
you, Socrates, whether you please or not, must continue to be a measure.
This is my defence, and I must request you to meet me fairly. We are
professing to reason, and not merely to dispute; and there is a great
difference between reasoning and disputation. For the disputer is always
seeking to trip up his opponent; and this is a mode of argument which
disgusts men with philosophy as they grow older. But the reasoner is
trying to understand him and to point out his errors to him, whether
arising from his own or from his companion's fault; he does not argue from
the customary use of names, which the vulgar pervert in all manner of ways.
If you are gentle to an adversary he will follow and love you; and if
defeated he will lay the blame on himself, and seek to escape from his own
prejudices into philosophy. I would recommend you, Socrates, to adopt this
humaner method, and to avoid captious and verbal criticisms.'

Such, Theodorus, is the very slight help which I am able to afford to your
friend; had he been alive, he would have helped himself in far better

'You have made a most valorous defence.'

Yes; but did you observe that Protagoras bade me be serious, and complained
of our getting up a laugh against him with the aid of a boy? He meant to
intimate that you must take the place of Theaetetus, who may be wiser than
many bearded men, but not wiser than you, Theodorus.

'The rule of the Spartan Palaestra is, Strip or depart; but you are like
the giant Antaeus, and will not let me depart unless I try a fall with

Yes, that is the nature of my complaint. And many a Hercules, many a
Theseus mighty in deeds and words has broken my head; but I am always at
this rough game. Please, then, to favour me.

'On the condition of not exceeding a single fall, I consent.'

Socrates now resumes the argument. As he is very desirous of doing justice
to Protagoras, he insists on citing his own words,--'What appears to each
man is to him.' And how, asks Socrates, are these words reconcileable with
the fact that all mankind are agreed in thinking themselves wiser than
others in some respects, and inferior to them in others? In the hour of
danger they are ready to fall down and worship any one who is their
superior in wisdom as if he were a god. And the world is full of men who
are asking to be taught and willing to be ruled, and of other men who are
willing to rule and teach them. All which implies that men do judge of one
another's impressions, and think some wise and others foolish. How will
Protagoras answer this argument? For he cannot say that no one deems
another ignorant or mistaken. If you form a judgment, thousands and tens
of thousands are ready to maintain the opposite. The multitude may not and
do not agree in Protagoras' own thesis that 'Man is the measure of all
things;' and then who is to decide? Upon his own showing must not his
'truth' depend on the number of suffrages, and be more or less true in
proportion as he has more or fewer of them? And he must acknowledge
further, that they speak truly who deny him to speak truly, which is a
famous jest. And if he admits that they speak truly who deny him to speak
truly, he must admit that he himself does not speak truly. But his
opponents will refuse to admit this of themselves, and he must allow that
they are right in their refusal. The conclusion is, that all mankind,
including Protagoras himself, will deny that he speaks truly; and his truth
will be true neither to himself nor to anybody else.

Theodorus is inclined to think that this is going too far. Socrates
ironically replies, that he is not going beyond the truth. But if the old
Protagoras could only pop his head out of the world below, he would
doubtless give them both a sound castigation and be off to the shades in an
instant. Seeing that he is not within call, we must examine the question
for ourselves. It is clear that there are great differences in the
understandings of men. Admitting, with Protagoras, that immediate
sensations of hot, cold, and the like, are to each one such as they appear,
yet this hypothesis cannot be extended to judgments or opinions. And even
if we were to admit further,--and this is the view of some who are not
thorough-going followers of Protagoras,--that right and wrong, holy and
unholy, are to each state or individual such as they appear, still
Protagoras will not venture to maintain that every man is equally the
measure of expediency, or that the thing which seems is expedient to every
one. But this begins a new question. 'Well, Socrates, we have plenty of
leisure. Yes, we have, and, after the manner of philosophers, we are
digressing; I have often observed how ridiculous this habit of theirs makes
them when they appear in court. 'What do you mean?' I mean to say that a
philosopher is a gentleman, but a lawyer is a servant. The one can have
his talk out, and wander at will from one subject to another, as the fancy
takes him; like ourselves, he may be long or short, as he pleases. But the
lawyer is always in a hurry; there is the clepsydra limiting his time, and
the brief limiting his topics, and his adversary is standing over him and
exacting his rights. He is a servant disputing about a fellow-servant
before his master, who holds the cause in his hands; the path never
diverges, and often the race is for his life. Such experiences render him
keen and shrewd; he learns the arts of flattery, and is perfect in the
practice of crooked ways; dangers have come upon him too soon, when the
tenderness of youth was unable to meet them with truth and honesty, and he
has resorted to counter-acts of dishonesty and falsehood, and become warped
and distorted; without any health or freedom or sincerity in him he has
grown up to manhood, and is or esteems himself to be a master of cunning.
Such are the lawyers; will you have the companion picture of philosophers?
or will this be too much of a digression?

'Nay, Socrates, the argument is our servant, and not our master. Who is
the judge or where is the spectator, having a right to control us?'

I will describe the leaders, then: for the inferior sort are not worth the
trouble. The lords of philosophy have not learned the way to the dicastery
or ecclesia; they neither see nor hear the laws and votes of the state,
written or recited; societies, whether political or festive, clubs, and
singing maidens do not enter even into their dreams. And the scandals of
persons or their ancestors, male and female, they know no more than they
can tell the number of pints in the ocean. Neither are they conscious of
their own ignorance; for they do not practise singularity in order to gain
reputation, but the truth is, that the outer form of them only is residing
in the city; the inner man, as Pindar says, is going on a voyage of
discovery, measuring as with line and rule the things which are under and
in the earth, interrogating the whole of nature, only not condescending to
notice what is near them.

'What do you mean, Socrates?'

I will illustrate my meaning by the jest of the witty maid-servant, who saw
Thales tumbling into a well, and said of him, that he was so eager to know
what was going on in heaven, that he could not see what was before his
feet. This is applicable to all philosophers. The philosopher is
unacquainted with the world; he hardly knows whether his neighbour is a man
or an animal. For he is always searching into the essence of man, and
enquiring what such a nature ought to do or suffer different from any
other. Hence, on every occasion in private life and public, as I was
saying, when he appears in a law-court or anywhere, he is the joke, not
only of maid-servants, but of the general herd, falling into wells and
every sort of disaster; he looks such an awkward, inexperienced creature,
unable to say anything personal, when he is abused, in answer to his
adversaries (for he knows no evil of any one); and when he hears the
praises of others, he cannot help laughing from the bottom of his soul at
their pretensions; and this also gives him a ridiculous appearance. A king
or tyrant appears to him to be a kind of swine-herd or cow-herd, milking
away at an animal who is much more troublesome and dangerous than cows or
sheep; like the cow-herd, he has no time to be educated, and the pen in
which he keeps his flock in the mountains is surrounded by a wall. When he
hears of large landed properties of ten thousand acres or more, he thinks
of the whole earth; or if he is told of the antiquity of a family, he
remembers that every one has had myriads of progenitors, rich and poor,
Greeks and barbarians, kings and slaves. And he who boasts of his descent
from Amphitryon in the twenty-fifth generation, may, if he pleases, add as
many more, and double that again, and our philosopher only laughs at his
inability to do a larger sum. Such is the man at whom the vulgar scoff; he
seems to them as if he could not mind his feet. 'That is very true,
Socrates.' But when he tries to draw the quick-witted lawyer out of his
pleas and rejoinders to the contemplation of absolute justice or injustice
in their own nature, or from the popular praises of wealthy kings to the
view of happiness and misery in themselves, or to the reasons why a man
should seek after the one and avoid the other, then the situation is
reversed; the little wretch turns giddy, and is ready to fall over the
precipice; his utterance becomes thick, and he makes himself ridiculous,
not to servant-maids, but to every man of liberal education. Such are the
two pictures: the one of the philosopher and gentleman, who may be excused
for not having learned how to make a bed, or cook up flatteries; the other,
a serviceable knave, who hardly knows how to wear his cloak,--still less
can he awaken harmonious thoughts or hymn virtue's praises.

'If the world, Socrates, were as ready to receive your words as I am, there
would be greater peace and less evil among mankind.'

Evil, Theodorus, must ever remain in this world to be the antagonist of
good, out of the way of the gods in heaven. Wherefore also we should fly
away from ourselves to them; and to fly to them is to become like them; and
to become like them is to become holy, just and true. But many live in the
old wives' fable of appearances; they think that you should follow virtue
in order that you may seem to be good. And yet the truth is, that God is
righteous; and of men, he is most like him who is most righteous. To know
this is wisdom; and in comparison of this the wisdom of the arts or the
seeming wisdom of politicians is mean and common. The unrighteous man is
apt to pride himself on his cunning; when others call him rogue, he says to
himself: 'They only mean that I am one who deserves to live, and not a
mere burden of the earth.' But he should reflect that his ignorance makes
his condition worse than if he knew. For the penalty of injustice is not
death or stripes, but the fatal necessity of becoming more and more unjust.
Two patterns of life are set before him; the one blessed and divine, the
other godless and wretched; and he is growing more and more like the one
and unlike the other. He does not see that if he continues in his cunning,
the place of innocence will not receive him after death. And yet if such a
man has the courage to hear the argument out, he often becomes dissatisfied
with himself, and has no more strength in him than a child.--But we have
digressed enough.

'For my part, Socrates, I like the digressions better than the argument,
because I understand them better.'

To return. When we left off, the Protagoreans and Heracliteans were
maintaining that the ordinances of the State were just, while they lasted.
But no one would maintain that the laws of the State were always good or
expedient, although this may be the intention of them. For the expedient
has to do with the future, about which we are liable to mistake. Now,
would Protagoras maintain that man is the measure not only of the present
and past, but of the future; and that there is no difference in the
judgments of men about the future? Would an untrained man, for example, be
as likely to know when he is going to have a fever, as the physician who
attended him? And if they differ in opinion, which of them is likely to be
right; or are they both right? Is not a vine-grower a better judge of a
vintage which is not yet gathered, or a cook of a dinner which is in
preparation, or Protagoras of the probable effect of a speech than an
ordinary person? The last example speaks 'ad hominen.' For Protagoras
would never have amassed a fortune if every man could judge of the future
for himself. He is, therefore, compelled to admit that he is a measure;
but I, who know nothing, am not equally convinced that I am. This is one
way of refuting him; and he is refuted also by the authority which he
attributes to the opinions of others, who deny his opinions. I am not
equally sure that we can disprove the truth of immediate states of feeling.
But this leads us to the doctrine of the universal flux, about which a
battle-royal is always going on in the cities of Ionia. 'Yes; the
Ephesians are downright mad about the flux; they cannot stop to argue with
you, but are in perpetual motion, obedient to their text-books. Their
restlessness is beyond expression, and if you ask any of them a question,
they will not answer, but dart at you some unintelligible saying, and
another and another, making no way either with themselves or with others;
for nothing is fixed in them or their ideas,--they are at war with fixed
principles.' I suppose, Theodorus, that you have never seen them in time
of peace, when they discourse at leisure to their disciples? 'Disciples!
they have none; they are a set of uneducated fanatics, and each of them
says of the other that they have no knowledge. We must trust to ourselves,
and not to them for the solution of the problem.' Well, the doctrine is
old, being derived from the poets, who speak in a figure of Oceanus and
Tethys; the truth was once concealed, but is now revealed by the superior
wisdom of a later generation, and made intelligible to the cobbler, who, on
hearing that all is in motion, and not some things only, as he ignorantly
fancied, may be expected to fall down and worship his teachers. And the
opposite doctrine must not be forgotten:--

'Alone being remains unmoved which is the name for all,'

as Parmenides affirms. Thus we are in the midst of the fray; both parties
are dragging us to their side; and we are not certain which of them are in
the right; and if neither, then we shall be in a ridiculous position,
having to set up our own opinion against ancient and famous men.

Let us first approach the river-gods, or patrons of the flux.

When they speak of motion, must they not include two kinds of motion,
change of place and change of nature?--And all things must be supposed to
have both kinds of motion; for if not, the same things would be at rest and
in motion, which is contrary to their theory. And did we not say, that all
sensations arise thus: they move about between the agent and patient
together with a perception, and the patient ceases to be a perceiving power
and becomes a percipient, and the agent a quale instead of a quality; but
neither has any absolute existence? But now we make the further discovery,
that neither white or whiteness, nor any sense or sensation, can be
predicated of anything, for they are in a perpetual flux. And therefore we
must modify the doctrine of Theaetetus and Protagoras, by asserting further
that knowledge is and is not sensation; and of everything we must say
equally, that this is and is not, or becomes or becomes not. And still the
word 'this' is not quite correct, for language fails in the attempt to
express their meaning.

At the close of the discussion, Theodorus claims to be released from the
argument, according to his agreement. But Theaetetus insists that they
shall proceed to consider the doctrine of rest. This is declined by
Socrates, who has too much reverence for the great Parmenides lightly to
attack him. (We shall find that he returns to the doctrine of rest in the
Sophist; but at present he does not wish to be diverted from his main
purpose, which is, to deliver Theaetetus of his conception of knowledge.)
He proceeds to interrogate him further. When he says that 'knowledge is in
perception,' with what does he perceive? The first answer is, that he
perceives sights with the eye, and sounds with the ear. This leads
Socrates to make the reflection that nice distinctions of words are
sometimes pedantic, but sometimes necessary; and he proposes in this case
to substitute the word 'through' for 'with.' For the senses are not like
the Trojan warriors in the horse, but have a common centre of perception,
in which they all meet. This common principle is able to compare them with
one another, and must therefore be distinct from them (compare Republic).
And as there are facts of sense which are perceived through the organs of
the body, there are also mathematical and other abstractions, such as
sameness and difference, likeness and unlikeness, which the soul perceives
by herself. Being is the most universal of these abstractions. The good
and the beautiful are abstractions of another kind, which exist in relation
and which above all others the mind perceives in herself, comparing within
her past, present, and future. For example; we know a thing to be hard or
soft by the touch, of which the perception is given at birth to men and
animals. But the essence of hardness or softness, or the fact that this
hardness is, and is the opposite of softness, is slowly learned by
reflection and experience. Mere perception does not reach being, and
therefore fails of truth; and therefore has no share in knowledge. But if
so, knowledge is not perception. What then is knowledge? The mind, when
occupied by herself with being, is said to have opinion--shall we say that
'Knowledge is true opinion'? But still an old difficulty recurs; we ask
ourselves, 'How is false opinion possible?' This difficulty may be stated
as follows:--

Either we know or do not know a thing (for the intermediate processes of
learning and forgetting need not at present be considered); and in thinking
or having an opinion, we must either know or not know that which we think,
and we cannot know and be ignorant at the same time; we cannot confuse one
thing which we do not know, with another thing which we do not know; nor
can we think that which we do not know to be that which we know, or that
which we know to be that which we do not know. And what other case is
conceivable, upon the supposition that we either know or do not know all
things? Let us try another answer in the sphere of being: 'When a man
thinks, and thinks that which is not.' But would this hold in any parallel
case? Can a man see and see nothing? or hear and hear nothing? or touch
and touch nothing? Must he not see, hear, or touch some one existing
thing? For if he thinks about nothing he does not think, and not thinking
he cannot think falsely. And so the path of being is closed against us, as
well as the path of knowledge. But may there not be 'heterodoxy,' or
transference of opinion;--I mean, may not one thing be supposed to be
another? Theaetetus is confident that this must be 'the true falsehood,'
when a man puts good for evil or evil for good. Socrates will not
discourage him by attacking the paradoxical expression 'true falsehood,'
but passes on. The new notion involves a process of thinking about two
things, either together or alternately. And thinking is the conversing of
the mind with herself, which is carried on in question and answer, until
she no longer doubts, but determines and forms an opinion. And false
opinion consists in saying to yourself, that one thing is another. But did
you ever say to yourself, that good is evil, or evil good? Even in sleep,
did you ever imagine that odd was even? Or did any man in his senses ever
fancy that an ox was a horse, or that two are one? So that we can never
think one thing to be another; for you must not meet me with the verbal
quibble that one--eteron--is other--eteron (both 'one' and 'other' in Greek
are called 'other'--eteron). He who has both the two things in his mind,
cannot misplace them; and he who has only one of them in his mind, cannot
misplace them--on either supposition transplacement is inconceivable.

But perhaps there may still be a sense in which we can think that which we
do not know to be that which we know: e.g. Theaetetus may know Socrates,
but at a distance he may mistake another person for him. This process may
be conceived by the help of an image. Let us suppose that every man has in
his mind a block of wax of various qualities, the gift of Memory, the
mother of the Muses; and on this he receives the seal or stamp of those
sensations and perceptions which he wishes to remember. That which he
succeeds in stamping is remembered and known by him as long as the
impression lasts; but that, of which the impression is rubbed out or
imperfectly made, is forgotten, and not known. No one can think one thing
to be another, when he has the memorial or seal of both of these in his
soul, and a sensible impression of neither; or when he knows one and does
not know the other, and has no memorial or seal of the other; or when he
knows neither; or when he perceives both, or one and not the other, or
neither; or when he perceives and knows both, and identifies what he
perceives with what he knows (this is still more impossible); or when he
does not know one, and does not know and does not perceive the other; or
does not perceive one, and does not know and does not perceive the other;
or has no perception or knowledge of either--all these cases must be
excluded. But he may err when he confuses what he knows or perceives, or
what he perceives and does not know, with what he knows, or what he knows
and perceives with what he knows and perceives.

Theaetetus is unable to follow these distinctions; which Socrates proceeds
to illustrate by examples, first of all remarking, that knowledge may exist
without perception, and perception without knowledge. I may know Theodorus
and Theaetetus and not see them; I may see them, and not know them. 'That
I understand.' But I could not mistake one for the other if I knew you
both, and had no perception of either; or if I knew one only, and perceived
neither; or if I knew and perceived neither, or in any other of the
excluded cases. The only possibility of error is: 1st, when knowing you
and Theodorus, and having the impression of both of you on the waxen block,
I, seeing you both imperfectly and at a distance, put the foot in the wrong
shoe--that is to say, put the seal or stamp on the wrong object: or 2ndly,
when knowing both of you I only see one; or when, seeing and knowing you
both, I fail to identify the impression and the object. But there could be
no error when perception and knowledge correspond.

The waxen block in the heart of a man's soul, as I may say in the words of
Homer, who played upon the words ker and keros, may be smooth and deep, and
large enough, and then the signs are clearly marked and lasting, and do not
get confused. But in the 'hairy heart,' as the all-wise poet sings, when
the wax is muddy or hard or moist, there is a corresponding confusion and
want of retentiveness; in the muddy and impure there is indistinctness, and
still more in the hard, for there the impressions have no depth of wax, and
in the moist they are too soon effaced. Yet greater is the indistinctness
when they are all jolted together in a little soul, which is narrow and has
no room. These are the sort of natures which have false opinion; from
stupidity they see and hear and think amiss; and this is falsehood and
ignorance. Error, then, is a confusion of thought and sense.

Theaetetus is delighted with this explanation. But Socrates has no sooner
found the new solution than he sinks into a fit of despondency. For an
objection occurs to him:--May there not be errors where there is no
confusion of mind and sense? e.g. in numbers. No one can confuse the man
whom he has in his thoughts with the horse which he has in his thoughts,
but he may err in the addition of five and seven. And observe that these
are purely mental conceptions. Thus we are involved once more in the
dilemma of saying, either that there is no such thing as false opinion, or
that a man knows what he does not know.

We are at our wit's end, and may therefore be excused for making a bold
diversion. All this time we have been repeating the words 'know,'
'understand,' yet we do not know what knowledge is. 'Why, Socrates, how
can you argue at all without using them?' Nay, but the true hero of
dialectic would have forbidden me to use them until I had explained them.
And I must explain them now. The verb 'to know' has two senses, to have
and to possess knowledge, and I distinguish 'having' from 'possessing.' A
man may possess a garment which he does not wear; or he may have wild birds
in an aviary; these in one sense he possesses, and in another he has none
of them. Let this aviary be an image of the mind, as the waxen block was;
when we are young, the aviary is empty; after a time the birds are put in;
for under this figure we may describe different forms of knowledge;--there
are some of them in groups, and some single, which are flying about
everywhere; and let us suppose a hunt after the science of odd and even, or
some other science. The possession of the birds is clearly not the same as
the having them in the hand. And the original chase of them is not the
same as taking them in the hand when they are already caged.

This distinction between use and possession saves us from the absurdity of
supposing that we do not know what we know, because we may know in one
sense, i.e. possess, what we do not know in another, i.e. use. But have we
not escaped one difficulty only to encounter a greater? For how can the
exchange of two kinds of knowledge ever become false opinion? As well
might we suppose that ignorance could make a man know, or that blindness
could make him see. Theaetetus suggests that in the aviary there may be
flying about mock birds, or forms of ignorance, and we put forth our hands
and grasp ignorance, when we are intending to grasp knowledge. But how can
he who knows the forms of knowledge and the forms of ignorance imagine one
to be the other? Is there some other form of knowledge which distinguishes
them? and another, and another? Thus we go round and round in a circle and
make no progress.

All this confusion arises out of our attempt to explain false opinion
without having explained knowledge. What then is knowledge? Theaetetus
repeats that knowledge is true opinion. But this seems to be refuted by
the instance of orators and judges. For surely the orator cannot convey a
true knowledge of crimes at which the judges were not present; he can only
persuade them, and the judge may form a true opinion and truly judge. But
if true opinion were knowledge they could not have judged without

Once more. Theaetetus offers a definition which he has heard: Knowledge
is true opinion accompanied by definition or explanation. Socrates has had
a similar dream, and has further heard that the first elements are names
only, and that definition or explanation begins when they are combined; the
letters are unknown, the syllables or combinations are known. But this new
hypothesis when tested by the letters of the alphabet is found to break
down. The first syllable of Socrates' name is SO. But what is SO? Two
letters, S and O, a sibilant and a vowel, of which no further explanation
can be given. And how can any one be ignorant of either of them, and yet
know both of them? There is, however, another alternative:--We may suppose
that the syllable has a separate form or idea distinct from the letters or
parts. The all of the parts may not be the whole. Theaetetus is very much
inclined to adopt this suggestion, but when interrogated by Socrates he is
unable to draw any distinction between the whole and all the parts. And if
the syllables have no parts, then they are those original elements of which
there is no explanation. But how can the syllable be known if the letter
remains unknown? In learning to read as children, we are first taught the
letters and then the syllables. And in music, the notes, which are the
letters, have a much more distinct meaning to us than the combination of

Once more, then, we must ask the meaning of the statement, that 'Knowledge
is right opinion, accompanied by explanation or definition.' Explanation
may mean, (1) the reflection or expression of a man's thoughts--but every
man who is not deaf and dumb is able to express his thoughts--or (2) the
enumeration of the elements of which anything is composed. A man may have
a true opinion about a waggon, but then, and then only, has he knowledge of
a waggon when he is able to enumerate the hundred planks of Hesiod. Or he
may know the syllables of the name Theaetetus, but not the letters; yet not
until he knows both can he be said to have knowledge as well as opinion.
But on the other hand he may know the syllable 'The' in the name
Theaetetus, yet he may be mistaken about the same syllable in the name
Theodorus, and in learning to read we often make such mistakes. And even
if he could write out all the letters and syllables of your name in order,
still he would only have right opinion. Yet there may be a third meaning
of the definition, besides the image or expression of the mind, and the
enumeration of the elements, viz. (3) perception of difference.

For example, I may see a man who has eyes, nose, and mouth;--that will not
distinguish him from any other man. Or he may have a snub-nose and
prominent eyes;--that will not distinguish him from myself and you and
others who are like me. But when I see a certain kind of snub-nosedness,
then I recognize Theaetetus. And having this sign of difference, I have
knowledge. But have I knowledge or opinion of this difference; if I have
only opinion I have not knowledge; if I have knowledge we assume a disputed
term; for knowledge will have to be defined as right opinion with knowledge
of difference.

And so, Theaetetus, knowledge is neither perception nor true opinion, nor
yet definition accompanying true opinion. And I have shown that the
children of your brain are not worth rearing. Are you still in labour, or
have you brought all you have to say about knowledge to the birth? If you
have any more thoughts, you will be the better for having got rid of these;
or if you have none, you will be the better for not fancying that you know
what you do not know. Observe the limits of my art, which, like my
mother's, is an art of midwifery; I do not pretend to compare with the good
and wise of this and other ages.

And now I go to meet Meletus at the porch of the King Archon; but to-morrow
I shall hope to see you again, Theodorus, at this place.


I. The saying of Theaetetus, that 'Knowledge is sensible perception,' may
be assumed to be a current philosophical opinion of the age. 'The
ancients,' as Aristotle (De Anim.) says, citing a verse of Empedocles,
'affirmed knowledge to be the same as perception.' We may now examine
these words, first, with reference to their place in the history of
philosophy, and secondly, in relation to modern speculations.

(a) In the age of Socrates the mind was passing from the object to the
subject. The same impulse which a century before had led men to form
conceptions of the world, now led them to frame general notions of the
human faculties and feelings, such as memory, opinion, and the like. The
simplest of these is sensation, or sensible perception, by which Plato
seems to mean the generalized notion of feelings and impressions of sense,
without determining whether they are conscious or not.

The theory that 'Knowledge is sensible perception' is the antithesis of
that which derives knowledge from the mind (Theaet.), or which assumes the
existence of ideas independent of the mind (Parm.). Yet from their extreme
abstraction these theories do not represent the opposite poles of thought
in the same way that the corresponding differences would in modern
philosophy. The most ideal and the most sensational have a tendency to
pass into one another; Heracleitus, like his great successor Hegel, has
both aspects. The Eleatic isolation of Being and the Megarian or Cynic
isolation of individuals are placed in the same class by Plato (Soph.); and
the same principle which is the symbol of motion to one mind is the symbol
of rest to another. The Atomists, who are sometimes regarded as the
Materialists of Plato, denied the reality of sensation. And in the ancient
as well as the modern world there were reactions from theory to experience,
from ideas to sense. This is a point of view from which the philosophy of
sensation presented great attraction to the ancient thinker. Amid the
conflict of ideas and the variety of opinions, the impression of sense
remained certain and uniform. Hardness, softness, cold, heat, etc. are not
absolutely the same to different persons, but the art of measuring could at
any rate reduce them all to definite natures (Republic). Thus the doctrine
that knowledge is perception supplies or seems to supply a firm standing
ground. Like the other notions of the earlier Greek philosophy, it was
held in a very simple way, without much basis of reasoning, and without
suggesting the questions which naturally arise in our own minds on the same

(b) The fixedness of impressions of sense furnishes a link of connexion
between ancient and modern philosophy. The modern thinker often repeats
the parallel axiom, 'All knowledge is experience.' He means to say that
the outward and not the inward is both the original source and the final
criterion of truth, because the outward can be observed and analyzed; the
inward is only known by external results, and is dimly perceived by each
man for himself. In what does this differ from the saying of Theaetetus?
Chiefly in this--that the modern term 'experience,' while implying a point
of departure in sense and a return to sense, also includes all the
processes of reasoning and imagination which have intervened. The
necessary connexion between them by no means affords a measure of the
relative degree of importance which is to be ascribed to either element.
For the inductive portion of any science may be small, as in mathematics or
ethics, compared with that which the mind has attained by reasoning and
reflection on a very few facts.

II. The saying that 'All knowledge is sensation' is identified by Plato
with the Protagorean thesis that 'Man is the measure of all things.' The
interpretation which Protagoras himself is supposed to give of these latter
words is: 'Things are to me as they appear to me, and to you as they
appear to you.' But there remains still an ambiguity both in the text and
in the explanation, which has to be cleared up. Did Protagoras merely mean
to assert the relativity of knowledge to the human mind? Or did he mean to
deny that there is an objective standard of truth?

These two questions have not been always clearly distinguished; the
relativity of knowledge has been sometimes confounded with uncertainty.
The untutored mind is apt to suppose that objects exist independently of
the human faculties, because they really exist independently of the
faculties of any individual. In the same way, knowledge appears to be a
body of truths stored up in books, which when once ascertained are
independent of the discoverer. Further consideration shows us that these
truths are not really independent of the mind; there is an adaptation of
one to the other, of the eye to the object of sense, of the mind to the
conception. There would be no world, if there neither were nor ever had
been any one to perceive the world. A slight effort of reflection enables
us to understand this; but no effort of reflection will enable us to pass
beyond the limits of our own faculties, or to imagine the relation or
adaptation of objects to the mind to be different from that of which we
have experience. There are certain laws of language and logic to which we
are compelled to conform, and to which our ideas naturally adapt
themselves; and we can no more get rid of them than we can cease to be
ourselves. The absolute and infinite, whether explained as self-existence,
or as the totality of human thought, or as the Divine nature, if known to
us at all, cannot escape from the category of relation.

But because knowledge is subjective or relative to the mind, we are not to
suppose that we are therefore deprived of any of the tests or criteria of
truth. One man still remains wiser than another, a more accurate observer
and relater of facts, a truer measure of the proportions of knowledge. The
nature of testimony is not altered, nor the verification of causes by
prescribed methods less certain. Again, the truth must often come to a man
through others, according to the measure of his capacity and education.
But neither does this affect the testimony, whether written or oral, which
he knows by experience to be trustworthy. He cannot escape from the laws
of his own mind; and he cannot escape from the further accident of being
dependent for his knowledge on others. But still this is no reason why he
should always be in doubt; of many personal, of many historical and
scientific facts he may be absolutely assured. And having such a mass of
acknowledged truth in the mathematical and physical, not to speak of the
moral sciences, the moderns have certainly no reason to acquiesce in the
statement that truth is appearance only, or that there is no difference
between appearance and truth.

The relativity of knowledge is a truism to us, but was a great
psychological discovery in the fifth century before Christ. Of this
discovery, the first distinct assertion is contained in the thesis of
Protagoras. Probably he had no intention either of denying or affirming an
objective standard of truth. He did not consider whether man in the higher
or man in the lower sense was a 'measure of all things.' Like other great
thinkers, he was absorbed with one idea, and that idea was the absoluteness
of perception. Like Socrates, he seemed to see that philosophy must be
brought back from 'nature' to 'truth,' from the world to man. But he did
not stop to analyze whether he meant 'man' in the concrete or man in the
abstract, any man or some men, 'quod semper quod ubique' or individual
private judgment. Such an analysis lay beyond his sphere of thought; the
age before Socrates had not arrived at these distinctions. Like the
Cynics, again, he discarded knowledge in any higher sense than perception.
For 'truer' or 'wiser' he substituted the word 'better,' and is not
unwilling to admit that both states and individuals are capable of
practical improvement. But this improvement does not arise from
intellectual enlightenment, nor yet from the exertion of the will, but from
a change of circumstances and impressions; and he who can effect this
change in himself or others may be deemed a philosopher. In the mode of
effecting it, while agreeing with Socrates and the Cynics in the importance
which he attaches to practical life, he is at variance with both of them.
To suppose that practice can be divorced from speculation, or that we may
do good without caring about truth, is by no means singular, either in
philosophy or life. The singularity of this, as of some other (so-called)
sophistical doctrines, is the frankness with which they are avowed, instead
of being veiled, as in modern times, under ambiguous and convenient

Plato appears to treat Protagoras much as he himself is treated by
Aristotle; that is to say, he does not attempt to understand him from his
own point of view. But he entangles him in the meshes of a more advanced
logic. To which Protagoras is supposed to reply by Megarian quibbles,
which destroy logic, 'Not only man, but each man, and each man at each
moment.' In the arguments about sight and memory there is a palpable
unfairness which is worthy of the great 'brainless brothers,' Euthydemus
and Dionysodorus, and may be compared with the egkekalummenos ('obvelatus')
of Eubulides. For he who sees with one eye only cannot be truly said both
to see and not to see; nor is memory, which is liable to forget, the
immediate knowledge to which Protagoras applies the term. Theodorus justly
charges Socrates with going beyond the truth; and Protagoras has equally
right on his side when he protests against Socrates arguing from the common
use of words, which 'the vulgar pervert in all manner of ways.'

III. The theory of Protagoras is connected by Aristotle as well as Plato
with the flux of Heracleitus. But Aristotle is only following Plato, and
Plato, as we have already seen, did not mean to imply that such a connexion
was admitted by Protagoras himself. His metaphysical genius saw or seemed
to see a common tendency in them, just as the modern historian of ancient
philosophy might perceive a parallelism between two thinkers of which they
were probably unconscious themselves. We must remember throughout that
Plato is not speaking of Heracleitus, but of the Heracliteans, who
succeeded him; nor of the great original ideas of the master, but of the
Eristic into which they had degenerated a hundred years later. There is
nothing in the fragments of Heracleitus which at all justifies Plato's
account of him. His philosophy may be resolved into two elements--first,
change, secondly, law or measure pervading the change: these he saw
everywhere, and often expressed in strange mythological symbols. But he
has no analysis of sensible perception such as Plato attributes to him; nor
is there any reason to suppose that he pushed his philosophy into that
absolute negation in which Heracliteanism was sunk in the age of Plato. He
never said that 'change means every sort of change;' and he expressly
distinguished between 'the general and particular understanding.' Like a
poet, he surveyed the elements of mythology, nature, thought, which lay
before him, and sometimes by the light of genius he saw or seemed to see a
mysterious principle working behind them. But as has been the case with
other great philosophers, and with Plato and Aristotle themselves, what was
really permanent and original could not be understood by the next
generation, while a perverted logic carried out his chance expressions with
an illogical consistency. His simple and noble thoughts, like those of the
great Eleatic, soon degenerated into a mere strife of words. And when thus
reduced to mere words, they seem to have exercised a far wider influence in
the cities of Ionia (where the people 'were mad about them') than in the
life-time of Heracleitus--a phenomenon which, though at first sight
singular, is not without a parallel in the history of philosophy and

It is this perverted form of the Heraclitean philosophy which is supposed
to effect the final overthrow of Protagorean sensationalism. For if all
things are changing at every moment, in all sorts of ways, then there is
nothing fixed or defined at all, and therefore no sensible perception, nor
any true word by which that or anything else can be described. Of course
Protagoras would not have admitted the justice of this argument any more
than Heracleitus would have acknowledged the 'uneducated fanatics' who
appealed to his writings. He might have said, 'The excellent Socrates has
first confused me with Heracleitus, and Heracleitus with his Ephesian
successors, and has then disproved the existence both of knowledge and
sensation. But I am not responsible for what I never said, nor will I
admit that my common-sense account of knowledge can be overthrown by
unintelligible Heraclitean paradoxes.'

IV. Still at the bottom of the arguments there remains a truth, that
knowledge is something more than sensible perception;--this alone would not
distinguish man from a tadpole. The absoluteness of sensations at each
moment destroys the very consciousness of sensations (compare Phileb.), or
the power of comparing them. The senses are not mere holes in a 'Trojan
horse,' but the organs of a presiding nature, in which they meet. A great
advance has been made in psychology when the senses are recognized as
organs of sense, and we are admitted to see or feel 'through them' and not
'by them,' a distinction of words which, as Socrates observes, is by no
means pedantic. A still further step has been made when the most abstract
notions, such as Being and Not-being, sameness and difference, unity and
plurality, are acknowledged to be the creations of the mind herself,
working upon the feelings or impressions of sense. In this manner Plato
describes the process of acquiring them, in the words 'Knowledge consists
not in the feelings or affections (pathemasi), but in the process of
reasoning about them (sullogismo).' Here, is in the Parmenides, he means
something not really different from generalization. As in the Sophist, he
is laying the foundation of a rational psychology, which is to supersede
the Platonic reminiscence of Ideas as well as the Eleatic Being and the
individualism of Megarians and Cynics.

V. Having rejected the doctrine that 'Knowledge is perception,' we now
proceed to look for a definition of knowledge in the sphere of opinion.
But here we are met by a singular difficulty: How is false opinion
possible? For we must either know or not know that which is presented to
the mind or to sense. We of course should answer at once: 'No; the
alternative is not necessary, for there may be degrees of knowledge; and we
may know and have forgotten, or we may be learning, or we may have a
general but not a particular knowledge, or we may know but not be able to
explain;' and many other ways may be imagined in which we know and do not
know at the same time. But these answers belong to a later stage of
metaphysical discussion; whereas the difficulty in question naturally
arises owing to the childhood of the human mind, like the parallel
difficulty respecting Not-being. Men had only recently arrived at the
notion of opinion; they could not at once define the true and pass beyond
into the false. The very word doxa was full of ambiguity, being sometimes,
as in the Eleatic philosophy, applied to the sensible world, and again used
in the more ordinary sense of opinion. There is no connexion between
sensible appearance and probability, and yet both of them met in the word
doxa, and could hardly be disengaged from one another in the mind of the
Greek living in the fifth or fourth century B.C. To this was often added,
as at the end of the fifth book of the Republic, the idea of relation,
which is equally distinct from either of them; also a fourth notion, the
conclusion of the dialectical process, the making up of the mind after she
has been 'talking to herself' (Theat.).

We are not then surprised that the sphere of opinion and of Not-being
should be a dusky, half-lighted place (Republic), belonging neither to the
old world of sense and imagination, nor to the new world of reflection and
reason. Plato attempts to clear up this darkness. In his accustomed
manner he passes from the lower to the higher, without omitting the
intermediate stages. This appears to be the reason why he seeks for the
definition of knowledge first in the sphere of opinion. Hereafter we shall
find that something more than opinion is required.

False opinion is explained by Plato at first as a confusion of mind and
sense, which arises when the impression on the mind does not correspond to
the impression made on the senses. It is obvious that this explanation
(supposing the distinction between impressions on the mind and impressions
on the senses to be admitted) does not account for all forms of error; and
Plato has excluded himself from the consideration of the greater number, by
designedly omitting the intermediate processes of learning and forgetting;
nor does he include fallacies in the use of language or erroneous
inferences. But he is struck by one possibility of error, which is not
covered by his theory, viz. errors in arithmetic. For in numbers and
calculation there is no combination of thought and sense, and yet errors
may often happen. Hence he is led to discard the explanation which might
nevertheless have been supposed to hold good (for anything which he says to
the contrary) as a rationale of error, in the case of facts derived from

Another attempt is made to explain false opinion by assigning to error a
sort of positive existence. But error or ignorance is essentially
negative--a not-knowing; if we knew an error, we should be no longer in
error. We may veil our difficulty under figures of speech, but these,
although telling arguments with the multitude, can never be the real
foundation of a system of psychology. Only they lead us to dwell upon
mental phenomena which if expressed in an abstract form would not be
realized by us at all. The figure of the mind receiving impressions is one
of those images which have rooted themselves for ever in language. It may
or may not be a 'gracious aid' to thought; but it cannot be got rid of.
The other figure of the enclosure is also remarkable as affording the first
hint of universal all-pervading ideas,--a notion further carried out in the
Sophist. This is implied in the birds, some in flocks, some solitary,
which fly about anywhere and everywhere. Plato discards both figures, as
not really solving the question which to us appears so simple: 'How do we
make mistakes?' The failure of the enquiry seems to show that we should
return to knowledge, and begin with that; and we may afterwards proceed,
with a better hope of success, to the examination of opinion.

But is true opinion really distinct from knowledge? The difference between
these he seeks to establish by an argument, which to us appears singular
and unsatisfactory. The existence of true opinion is proved by the
rhetoric of the law courts, which cannot give knowledge, but may give true
opinion. The rhetorician cannot put the judge or juror in possession of
all the facts which prove an act of violence, but he may truly persuade
them of the commission of such an act. Here the idea of true opinion seems
to be a right conclusion from imperfect knowledge. But the correctness of
such an opinion will be purely accidental; and is really the effect of one
man, who has the means of knowing, persuading another who has not. Plato
would have done better if he had said that true opinion was a contradiction
in terms.

Assuming the distinction between knowledge and opinion, Theaetetus, in
answer to Socrates, proceeds to define knowledge as true opinion, with
definite or rational explanation. This Socrates identifies with another
and different theory, of those who assert that knowledge first begins with
a proposition.

The elements may be perceived by sense, but they are names, and cannot be
defined. When we assign to them some predicate, they first begin to have a
meaning (onomaton sumploke logou ousia). This seems equivalent to saying,
that the individuals of sense become the subject of knowledge when they are
regarded as they are in nature in relation to other individuals.

Yet we feel a difficulty in following this new hypothesis. For must not
opinion be equally expressed in a proposition? The difference between true
and false opinion is not the difference between the particular and the
universal, but between the true universal and the false. Thought may be as
much at fault as sight. When we place individuals under a class, or assign
to them attributes, this is not knowledge, but a very rudimentary process
of thought; the first generalization of all, without which language would
be impossible. And has Plato kept altogether clear of a confusion, which
the analogous word logos tends to create, of a proposition and a
definition? And is not the confusion increased by the use of the analogous
term 'elements,' or 'letters'? For there is no real resemblance between
the relation of letters to a syllable, and of the terms to a proposition.

Plato, in the spirit of the Megarian philosophy, soon discovers a flaw in
the explanation. For how can we know a compound of which the simple
elements are unknown to us? Can two unknowns make a known? Can a whole be
something different from the parts? The answer of experience is that they
can; for we may know a compound, which we are unable to analyze into its
elements; and all the parts, when united, may be more than all the parts
separated: e.g. the number four, or any other number, is more than the
units which are contained in it; any chemical compound is more than and
different from the simple elements. But ancient philosophy in this, as in
many other instances, proceeding by the path of mental analysis, was
perplexed by doubts which warred against the plainest facts.

Three attempts to explain the new definition of knowledge still remain to
be considered. They all of them turn on the explanation of logos. The
first account of the meaning of the word is the reflection of thought in
speech--a sort of nominalism 'La science est une langue bien faite.' But
anybody who is not dumb can say what he thinks; therefore mere speech
cannot be knowledge. And yet we may observe, that there is in this
explanation an element of truth which is not recognized by Plato; viz. that
truth and thought are inseparable from language, although mere expression
in words is not truth. The second explanation of logos is the enumeration
of the elementary parts of the complex whole. But this is only definition
accompanied with right opinion, and does not yet attain to the certainty of
knowledge. Plato does not mention the greater objection, which is, that
the enumeration of particulars is endless; such a definition would be based
on no principle, and would not help us at all in gaining a common idea.
The third is the best explanation,--the possession of a characteristic
mark, which seems to answer to the logical definition by genus and
difference. But this, again, is equally necessary for right opinion; and
we have already determined, although not on very satisfactory grounds, that
knowledge must be distinguished from opinion. A better distinction is
drawn between them in the Timaeus. They might be opposed as philosophy and
rhetoric, and as conversant respectively with necessary and contingent
matter. But no true idea of the nature of either of them, or of their
relation to one another, could be framed until science obtained a content.
The ancient philosophers in the age of Plato thought of science only as
pure abstraction, and to this opinion stood in no relation.

Like Theaetetus, we have attained to no definite result. But an
interesting phase of ancient philosophy has passed before us. And the
negative result is not to be despised. For on certain subjects, and in
certain states of knowledge, the work of negation or clearing the ground
must go on, perhaps for a generation, before the new structure can begin to
rise. Plato saw the necessity of combating the illogical logic of the
Megarians and Eristics. For the completion of the edifice, he makes
preparation in the Theaetetus, and crowns the work in the Sophist.

Many (1) fine expressions, and (2) remarks full of wisdom, (3) also germs
of a metaphysic of the future, are scattered up and down in the dialogue.
Such, for example, as (1) the comparison of Theaetetus' progress in
learning to the 'noiseless flow of a river of oil'; the satirical touch,
'flavouring a sauce or fawning speech'; or the remarkable expression, 'full
of impure dialectic'; or the lively images under which the argument is
described,--'the flood of arguments pouring in,' the fresh discussions
'bursting in like a band of revellers.' (2) As illustrations of the second
head, may be cited the remark of Socrates, that 'distinctions of words,
although sometimes pedantic, are also necessary'; or the fine touch in the
character of the lawyer, that 'dangers came upon him when the tenderness of
youth was unequal to them'; or the description of the manner in which the
spirit is broken in a wicked man who listens to reproof until he becomes
like a child; or the punishment of the wicked, which is not physical
suffering, but the perpetual companionship of evil (compare Gorgias); or
the saying, often repeated by Aristotle and others, that 'philosophy begins
in wonder, for Iris is the child of Thaumas'; or the superb contempt with
which the philosopher takes down the pride of wealthy landed proprietors by
comparison of the whole earth. (3) Important metaphysical ideas are: a.
the conception of thought, as the mind talking to herself; b. the notion of
a common sense, developed further by Aristotle, and the explicit
declaration, that the mind gains her conceptions of Being, sameness,
number, and the like, from reflection on herself; c. the excellent
distinction of Theaetetus (which Socrates, speaking with emphasis, 'leaves
to grow') between seeing the forms or hearing the sounds of words in a
foreign language, and understanding the meaning of them; and d. the
distinction of Socrates himself between 'having' and 'possessing'
knowledge, in which the answer to the whole discussion appears to be


There is a difference between ancient and modern psychology, and we have a
difficulty in explaining one in the terms of the other. To us the inward
and outward sense and the inward and outward worlds of which they are the
organs are parted by a wall, and appear as if they could never be
confounded. The mind is endued with faculties, habits, instincts, and a
personality or consciousness in which they are bound together. Over
against these are placed forms, colours, external bodies coming into
contact with our own body. We speak of a subject which is ourselves, of an
object which is all the rest. These are separable in thought, but united
in any act of sensation, reflection, or volition. As there are various
degrees in which the mind may enter into or be abstracted from the
operations of sense, so there are various points at which this separation
or union may be supposed to occur. And within the sphere of mind the
analogy of sense reappears; and we distinguish not only external objects,
but objects of will and of knowledge which we contrast with them. These
again are comprehended in a higher object, which reunites with the subject.
A multitude of abstractions are created by the efforts of successive
thinkers which become logical determinations; and they have to be arranged
in order, before the scheme of thought is complete. The framework of the
human intellect is not the peculium of an individual, but the joint work of
many who are of all ages and countries. What we are in mind is due, not
merely to our physical, but to our mental antecedents which we trace in
history, and more especially in the history of philosophy. Nor can mental
phenomena be truly explained either by physiology or by the observation of
consciousness apart from their history. They have a growth of their own,
like the growth of a flower, a tree, a human being. They may be conceived
as of themselves constituting a common mind, and having a sort of personal
identity in which they coexist.

So comprehensive is modern psychology, seeming to aim at constructing anew
the entire world of thought. And prior to or simultaneously with this
construction a negative process has to be carried on, a clearing away of
useless abstractions which we have inherited from the past. Many erroneous
conceptions of the mind derived from former philosophies have found their
way into language, and we with difficulty disengage ourselves from them.
Mere figures of speech have unconsciously influenced the minds of great
thinkers. Also there are some distinctions, as, for example, that of the
will and of the reason, and of the moral and intellectual faculties, which
are carried further than is justified by experience. Any separation of
things which we cannot see or exactly define, though it may be necessary,
is a fertile source of error. The division of the mind into faculties or
powers or virtues is too deeply rooted in language to be got rid of, but it
gives a false impression. For if we reflect on ourselves we see that all
our faculties easily pass into one another, and are bound together in a
single mind or consciousness; but this mental unity is apt to be concealed
from us by the distinctions of language.

A profusion of words and ideas has obscured rather than enlightened mental
science. It is hard to say how many fallacies have arisen from the
representation of the mind as a box, as a 'tabula rasa,' a book, a mirror,
and the like. It is remarkable how Plato in the Theaetetus, after having
indulged in the figure of the waxen tablet and the decoy, afterwards
discards them. The mind is also represented by another class of images, as
the spring of a watch, a motive power, a breath, a stream, a succession of
points or moments. As Plato remarks in the Cratylus, words expressive of
motion as well as of rest are employed to describe the faculties and
operations of the mind; and in these there is contained another store of
fallacies. Some shadow or reflection of the body seems always to adhere to
our thoughts about ourselves, and mental processes are hardly distinguished
in language from bodily ones. To see or perceive are used indifferently of
both; the words intuition, moral sense, common sense, the mind's eye, are
figures of speech transferred from one to the other. And many other words
used in early poetry or in sacred writings to express the works of mind
have a materialistic sound; for old mythology was allied to sense, and the
distinction of matter and mind had not as yet arisen. Thus materialism
receives an illusive aid from language; and both in philosophy and religion
the imaginary figure or association easily takes the place of real

Again, there is the illusion of looking into our own minds as if our
thoughts or feelings were written down in a book. This is another figure
of speech, which might be appropriately termed 'the fallacy of the looking-
glass.' We cannot look at the mind unless we have the eye which sees, and
we can only look, not into, but out of the mind at the thoughts, words,
actions of ourselves and others. What we dimly recognize within us is not
experience, but rather the suggestion of an experience, which we may
gather, if we will, from the observation of the world. The memory has but
a feeble recollection of what we were saying or doing a few weeks or a few
months ago, and still less of what we were thinking or feeling. This is
one among many reasons why there is so little self-knowledge among mankind;
they do not carry with them the thought of what they are or have been. The
so-called 'facts of consciousness' are equally evanescent; they are facts
which nobody ever saw, and which can neither be defined nor described. Of
the three laws of thought the first (All A = A) is an identical
proposition--that is to say, a mere word or symbol claiming to be a
proposition: the two others (Nothing can be A and not A, and Everything is
either A or not A) are untrue, because they exclude degrees and also the
mixed modes and double aspects under which truth is so often presented to
us. To assert that man is man is unmeaning; to say that he is free or
necessary and cannot be both is a half truth only. These are a few of the
entanglements which impede the natural course of human thought. Lastly,
there is the fallacy which lies still deeper, of regarding the individual
mind apart from the universal, or either, as a self-existent entity apart
from the ideas which are contained in them.

In ancient philosophies the analysis of the mind is still rudimentary and
imperfect. It naturally began with an effort to disengage the universal
from sense--this was the first lifting up of the mist. It wavered between
object and subject, passing imperceptibly from one or Being to mind and
thought. Appearance in the outward object was for a time indistinguishable
from opinion in the subject. At length mankind spoke of knowing as well as
of opining or perceiving. But when the word 'knowledge' was found how was
it to be explained or defined? It was not an error, it was a step in the
right direction, when Protagoras said that 'Man is the measure of all
things,' and that 'All knowledge is perception.' This was the subjective
which corresponded to the objective 'All is flux.' But the thoughts of men
deepened, and soon they began to be aware that knowledge was neither sense,
nor yet opinion--with or without explanation; nor the expression of
thought, nor the enumeration of parts, nor the addition of characteristic
marks. Motion and rest were equally ill adapted to express its nature,
although both must in some sense be attributed to it; it might be described
more truly as the mind conversing with herself; the discourse of reason;
the hymn of dialectic, the science of relations, of ideas, of the so-called
arts and sciences, of the one, of the good, of the all:--this is the way
along which Plato is leading us in his later dialogues. In its higher
signification it was the knowledge, not of men, but of gods, perfect and
all sufficing:--like other ideals always passing out of sight, and
nevertheless present to the mind of Aristotle as well as Plato, and the
reality to which they were both tending. For Aristotle as well as Plato
would in modern phraseology have been termed a mystic; and like him would
have defined the higher philosophy to be 'Knowledge of being or essence,'--
words to which in our own day we have a difficulty in attaching a meaning.

Yet, in spite of Plato and his followers, mankind have again and again
returned to a sensational philosophy. As to some of the early thinkers,
amid the fleetings of sensible objects, ideas alone seemed to be fixed, so
to a later generation amid the fluctuation of philosophical opinions the
only fixed points appeared to be outward objects. Any pretence of
knowledge which went beyond them implied logical processes, of the
correctness of which they had no assurance and which at best were only
probable. The mind, tired of wandering, sought to rest on firm ground;
when the idols of philosophy and language were stripped off, the perception
of outward objects alone remained. The ancient Epicureans never asked
whether the comparison of these with one another did not involve principles
of another kind which were above and beyond them. In like manner the
modern inductive philosophy forgot to enquire into the meaning of
experience, and did not attempt to form a conception of outward objects
apart from the mind, or of the mind apart from them. Soon objects of sense
were merged in sensations and feelings, but feelings and sensations were
still unanalyzed. At last we return to the doctrine attributed by Plato to
Protagoras, that the mind is only a succession of momentary perceptions.
At this point the modern philosophy of experience forms an alliance with
ancient scepticism.

The higher truths of philosophy and religion are very far removed from
sense. Admitting that, like all other knowledge, they are derived from
experience, and that experience is ultimately resolvable into facts which
come to us through the eye and ear, still their origin is a mere accident
which has nothing to do with their true nature. They are universal and
unseen; they belong to all times--past, present, and future. Any worthy
notion of mind or reason includes them. The proof of them is, 1st, their
comprehensiveness and consistency with one another; 2ndly, their agreement
with history and experience. But sensation is of the present only, is
isolated, is and is not in successive moments. It takes the passing hour
as it comes, following the lead of the eye or ear instead of the command of
reason. It is a faculty which man has in common with the animals, and in
which he is inferior to many of them. The importance of the senses in us
is that they are the apertures of the mind, doors and windows through which
we take in and make our own the materials of knowledge. Regarded in any
other point of view sensation is of all mental acts the most trivial and
superficial. Hence the term 'sensational' is rightly used to express what
is shallow in thought and feeling.

We propose in what follows, first of all, like Plato in the Theaetetus, to
analyse sensation, and secondly to trace the connexion between theories of
sensation and a sensational or Epicurean philosophy.

Paragraph I. We, as well as the ancients, speak of the five senses, and of
a sense, or common sense, which is the abstraction of them. The term
'sense' is also used metaphorically, both in ancient and modern philosophy,
to express the operations of the mind which are immediate or intuitive. Of
the five senses, two--the sight and the hearing--are of a more subtle and
complex nature, while two others--the smell and the taste--seem to be only
more refined varieties of touch. All of them are passive, and by this are
distinguished from the active faculty of speech: they receive impressions,
but do not produce them, except in so far as they are objects of sense

Physiology speaks to us of the wonderful apparatus of nerves, muscles,
tissues, by which the senses are enabled to fulfil their functions. It
traces the connexion, though imperfectly, of the bodily organs with the
operations of the mind. Of these latter, it seems rather to know the
conditions than the causes. It can prove to us that without the brain we
cannot think, and that without the eye we cannot see: and yet there is far
more in thinking and seeing than is given by the brain and the eye. It
observes the 'concomitant variations' of body and mind. Psychology, on the
other hand, treats of the same subject regarded from another point of view.
It speaks of the relation of the senses to one another; it shows how they
meet the mind; it analyzes the transition from sense to thought. The one
describes their nature as apparent to the outward eye; by the other they
are regarded only as the instruments of the mind. It is in this latter
point of view that we propose to consider them.

The simplest sensation involves an unconscious or nascent operation of the
mind; it implies objects of sense, and objects of sense have differences of
form, number, colour. But the conception of an object without us, or the
power of discriminating numbers, forms, colours, is not given by the sense,
but by the mind. A mere sensation does not attain to distinctness: it is
a confused impression, sugkechumenon ti, as Plato says (Republic), until
number introduces light and order into the confusion. At what point
confusion becomes distinctness is a question of degree which cannot be
precisely determined. The distant object, the undefined notion, come out
into relief as we approach them or attend to them. Or we may assist the
analysis by attempting to imagine the world first dawning upon the eye of
the infant or of a person newly restored to sight. Yet even with them the
mind as well as the eye opens or enlarges. For all three are inseparably
bound together--the object would be nowhere and nothing, if not perceived
by the sense, and the sense would have no power of distinguishing without
the mind.

But prior to objects of sense there is a third nature in which they are
contained--that is to say, space, which may be explained in various ways.
It is the element which surrounds them; it is the vacuum or void which they
leave or occupy when passing from one portion of space to another. It
might be described in the language of ancient philosophy, as 'the Not-
being' of objects. It is a negative idea which in the course of ages has
become positive. It is originally derived from the contemplation of the
world without us--the boundless earth or sea, the vacant heaven, and is
therefore acquired chiefly through the sense of sight: to the blind the
conception of space is feeble and inadequate, derived for the most part
from touch or from the descriptions of others. At first it appears to be
continuous; afterwards we perceive it to be capable of division by lines or
points, real or imaginary. By the help of mathematics we form another idea
of space, which is altogether independent of experience. Geometry teaches
us that the innumerable lines and figures by which space is or may be
intersected are absolutely true in all their combinations and consequences.
New and unchangeable properties of space are thus developed, which are
proved to us in a thousand ways by mathematical reasoning as well as by
common experience. Through quantity and measure we are conducted to our
simplest and purest notion of matter, which is to the cube or solid what
space is to the square or surface. And all our applications of mathematics
are applications of our ideas of space to matter. No wonder then that they
seem to have a necessary existence to us. Being the simplest of our ideas,
space is also the one of which we have the most difficulty in ridding
ourselves. Neither can we set a limit to it, for wherever we fix a limit,
space is springing up beyond. Neither can we conceive a smallest or
indivisible portion of it; for within the smallest there is a smaller
still; and even these inconceivable qualities of space, whether the
infinite or the infinitesimal, may be made the subject of reasoning and
have a certain truth to us.

Whether space exists in the mind or out of it, is a question which has no
meaning. We should rather say that without it the mind is incapable of
conceiving the body, and therefore of conceiving itself. The mind may be
indeed imagined to contain the body, in the same way that Aristotle (partly
following Plato) supposes God to be the outer heaven or circle of the
universe. But how can the individual mind carry about the universe of
space packed up within, or how can separate minds have either a universe of
their own or a common universe? In such conceptions there seems to be a
confusion of the individual and the universal. To say that we can only
have a true idea of ourselves when we deny the reality of that by which we
have any idea of ourselves is an absurdity. The earth which is our
habitation and 'the starry heaven above' and we ourselves are equally an
illusion, if space is only a quality or condition of our minds.

Again, we may compare the truths of space with other truths derived from
experience, which seem to have a necessity to us in proportion to the
frequency of their recurrence or the truth of the consequences which may be
inferred from them. We are thus led to remark that the necessity in our
ideas of space on which much stress has been laid, differs in a slight
degree only from the necessity which appears to belong to other of our
ideas, e.g. weight, motion, and the like. And there is another way in
which this necessity may be explained. We have been taught it, and the
truth which we were taught or which we inherited has never been
contradicted in all our experience and is therefore confirmed by it. Who
can resist an idea which is presented to him in a general form in every
moment of his life and of which he finds no instance to the contrary? The
greater part of what is sometimes regarded as the a priori intuition of
space is really the conception of the various geometrical figures of which
the properties have been revealed by mathematical analysis. And the
certainty of these properties is immeasurably increased to us by our
finding that they hold good not only in every instance, but in all the
consequences which are supposed to flow from them.

Neither must we forget that our idea of space, like our other ideas, has a
history. The Homeric poems contain no word for it; even the later Greek
philosophy has not the Kantian notion of space, but only the definite
'place' or 'the infinite.' To Plato, in the Timaeus, it is known only as
the 'nurse of generation.' When therefore we speak of the necessity of our
ideas of space we must remember that this is a necessity which has grown up
with the growth of the human mind, and has been made by ourselves. We can
free ourselves from the perplexities which are involved in it by ascending
to a time in which they did not as yet exist. And when space or time are
described as 'a priori forms or intuitions added to the matter given in
sensation,' we should consider that such expressions belong really to the
'pre-historic study' of philosophy, i.e. to the eighteenth century, when
men sought to explain the human mind without regard to history or language
or the social nature of man.

In every act of sense there is a latent perception of space, of which we
only become conscious when objects are withdrawn from it. There are
various ways in which we may trace the connexion between them. We may
think of space as unresisting matter, and of matter as divided into
objects; or of objects again as formed by abstraction into a collective
notion of matter, and of matter as rarefied into space. And motion may be
conceived as the union of there and not there in space, and force as the
materializing or solidification of motion. Space again is the individual
and universal in one; or, in other words, a perception and also a
conception. So easily do what are sometimes called our simple ideas pass
into one another, and differences of kind resolve themselves into
differences of degree.

Within or behind space there is another abstraction in many respects
similar to it--time, the form of the inward, as space is the form of the
outward. As we cannot think of outward objects of sense or of outward
sensations without space, so neither can we think of a succession of
sensations without time. It is the vacancy of thoughts or sensations, as
space is the void of outward objects, and we can no more imagine the mind
without the one than the world without the other. It is to arithmetic what
space is to geometry; or, more strictly, arithmetic may be said to be
equally applicable to both. It is defined in our minds, partly by the
analogy of space and partly by the recollection of events which have
happened to us, or the consciousness of feelings which we are experiencing.
Like space, it is without limit, for whatever beginning or end of time we
fix, there is a beginning and end before them, and so on without end. We
speak of a past, present, and future, and again the analogy of space
assists us in conceiving of them as coexistent. When the limit of time is
removed there arises in our minds the idea of eternity, which at first,
like time itself, is only negative, but gradually, when connected with the
world and the divine nature, like the other negative infinity of space,
becomes positive. Whether time is prior to the mind and to experience, or
coeval with them, is (like the parallel question about space) unmeaning.
Like space it has been realized gradually: in the Homeric poems, or even
in the Hesiodic cosmogony, there is no more notion of time than of space.
The conception of being is more general than either, and might therefore
with greater plausibility be affirmed to be a condition or quality of the
mind. The a priori intuitions of Kant would have been as unintelligible to
Plato as his a priori synthetical propositions to Aristotle. The
philosopher of Konigsberg supposed himself to be analyzing a necessary mode
of thought: he was not aware that he was dealing with a mere abstraction.
But now that we are able to trace the gradual developement of ideas through
religion, through language, through abstractions, why should we interpose

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