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The Analysis of Mind

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animal is reflective, like some men, it comes to think that it
had the final situation in mind throughout; sometimes it comes to
know what situation will bring satisfaction, so that in fact the
discomfort does bring the thought of what will allay it.
Nevertheless the sensation involving discomfort remains the prime

This brings us to the question of the nature of discomfort and
pleasure. Since Kant it has been customary to recognize three
great divisions of mental phenomena, which are typified by
knowledge, desire and feeling, where "feeling" is used to mean
pleasure and discomfort. Of course, "knowledge" is too definite a
word: the states of mind concerned are grouped together as
"cognitive," and are to embrace not only beliefs, but
perceptions, doubts, and the understanding of concepts. "Desire,"
also, is narrower than what is intended: for example, WILL is to
be included in this category, and in fact every thing that
involves any kind of striving, or "conation" as it is technically
called. I do not myself believe that there is any value in this
threefold division of the contents of mind. I believe that
sensations (including images) supply all the "stuff" of the mind,
and that everything else can be analysed into groups of
sensations related in various ways, or characteristics of
sensations or of groups of sensations. As regards belief, I shall
give grounds for this view in later lectures. As regards desires,
I have given some grounds in this lecture. For the present, it is
pleasure and discomfort that concern us. There are broadly three
theories that might be held in regard to them. We may regard them
as separate existing items in those who experience them, or we
may regard them as intrinsic qualities of sensations and other
mental occurrences, or we may regard them as mere names for the
causal characteristics of the occurrences which are uncomfortable
or pleasant. The first of these theories, namely, that which
regards discomfort and pleasure as actual contents in those who
experience them, has, I think, nothing conclusive to be said in
its favour.* It is suggested chiefly by an ambiguity in the word
"pain," which has misled many people, including Berkeley, whom it
supplied with one of his arguments for subjective idealism. We
may use "pain" as the opposite of "pleasure," and "painful" as
the opposite of "pleasant," or we may use "pain" to mean a
certain sort of sensation, on a level with the sensations of heat
and cold and touch. The latter use of the word has prevailed in
psychological literature, and it is now no longer used as the
opposite of "pleasure." Dr. H. Head, in a recent publication, has
stated this distinction as follows:**

* Various arguments in its favour are advanced by A. Wohlgemuth,
"On the feelings and their neural correlate, with an examination
of the nature of pain," "British Journal of Psychology," viii, 4.
(1917). But as these arguments are largely a reductio ad absurdum
of other theories, among which that which I am advocating is not
included, I cannot regard them as establishing their contention.

** "Sensation and the Cerebral Cortex," "Brain," vol. xli, part
ii (September, 1918), p. 90. Cf. also Wohlgemuth, loc. cit. pp.
437, 450.

"It is necessary at the outset to distinguish clearly between
'discomfort' and 'pain.' Pain is a distinct sensory quality
equivalent to heat and cold, and its intensity can be roughly
graded according to the force expended in stimulation.
Discomfort, on the other hand, is that feeling-tone which is
directly opposed to pleasure. It may accompany sensations not in
themselves essentially painful; as for instance that produced by
tickling the sole of the foot. The reaction produced by repeated
pricking contains both these elements; for it evokes that sensory
quality known as pain, accompanied by a disagreeable
feeling-tone, which we have called discomfort. On the other hand,
excessive pressure, except when applied directly over some
nerve-trunk, tends to excite more discomfort than pain."

The confusion between discomfort and pain has made people regard
discomfort as a more substantial thing than it is, and this in
turn has reacted upon the view taken of pleasure, since
discomfort and pleasure are evidently on a level in this respect.
As soon as discomfort is clearly distinguished from the sensation
of pain, it becomes more natural to regard discomfort and
pleasure as properties of mental occurrences than to regard them
as separate mental occurrences on their own account. I shall
therefore dismiss the view that they are separate mental
occurrences, and regard them as properties of such experiences as
would be called respectively uncomfortable and pleasant.

It remains to be examined whether they are actual qualities of
such occurrences, or are merely differences as to causal
properties. I do not myself see any way of deciding this
question; either view seems equally capable of accounting for the
facts. If this is true, it is safer to avoid the assumption that
there are such intrinsic qualities of mental occurrences as are
in question, and to assume only the causal differences which are
undeniable. Without condemning the intrinsic theory, we can
define discomfort and pleasure as consisting in causal
properties, and say only what will hold on either of the two
theories. Following this course, we shall say:

"Discomfort" is a property of a sensation or other mental
occurrence, consisting in the fact that the occurrence in
question stimulates voluntary or reflex movements tending to
produce some more or less definite change involving the cessation
of the occurrence.

"Pleasure" is a property of a sensation or other mental
occurrence, consisting in the fact that the occurrence in
question either does not stimulate any voluntary or reflex
movement, or, if it does, stimulates only such as tend to prolong
the occurrence in question.*

* Cf. Thorndike, op. cit., p. 243.

"Conscious" desire, which we have now to consider, consists of
desire in the sense hitherto discussed, together with a true
belief as to its "purpose," i.e. as to the state of affairs that
will bring quiescence with cessation of the discomfort. If our
theory of desire is correct, a belief as to its purpose may very
well be erroneous, since only experience can show what causes a
discomfort to cease. When the experience needed is common and
simple, as in the case of hunger, a mistake is not very probable.
But in other cases--e.g. erotic desire in those who have had
little or no experience of its satisfaction--mistakes are to be
expected, and do in fact very often occur. The practice of
inhibiting impulses, which is to a great extent necessary to
civilized life, makes mistakes easier, by preventing experience
of the actions to which a desire would otherwise lead, and by
often causing the inhibited impulses themselves to be unnoticed
or quickly forgotten. The perfectly natural mistakes which thus
arise constitute a large proportion of what is, mistakenly in
part, called self-deception, and attributed by Freud to the

But there is a further point which needs emphasizing, namely,
that a belief that something is desired has often a tendency to
cause the very desire that is believed in. It is this fact that
makes the effect of "consciousness" on desire so complicated.

When we believe that we desire a certain state of affairs, that
often tends to cause a real desire for it. This is due partly to
the influence of words upon our emotions, in rhetoric for
example, and partly to the general fact that discomfort normally
belongs to the belief that we desire such-and-such a thing that
we do not possess. Thus what was originally a false opinion as to
the object of a desire acquires a certain truth: the false
opinion generates a secondary subsidiary desire, which
nevertheless becomes real. Let us take an illustration. Suppose
you have been jilted in a way which wounds your vanity. Your
natural impulsive desire will be of the sort expressed in Donne's

When by thy scorn, O Murderess, I am dead,

in which he explains how he will haunt the poor lady as a ghost,
and prevent her from enjoying a moment's peace. But two things
stand in the way of your expressing yourself so naturally: on the
one hand, your vanity, which will not acknowledge how hard you
are hit; on the other hand, your conviction that you are a
civilized and humane person, who could not possibly indulge so
crude a desire as revenge. You will therefore experience a
restlessness which will at first seem quite aimless, but will
finally resolve itself in a conscious desire to change your
profession, or go round the world, or conceal your identity and
live in Putney, like Arnold Bennett's hero. Although the prime
cause of this desire is a false judgment as to your previous
unconscious desire, yet the new conscious desire has its own
derivative genuineness, and may influence your actions to the
extent of sending you round the world. The initial mistake,
however, will have effects of two kinds. First, in uncontrolled
moments, under the influence of sleepiness or drink or delirium,
you will say things calculated to injure the faithless deceiver.
Secondly, you will find travel disappointing, and the East less
fascinating than you had hoped--unless, some day, you hear that
the wicked one has in turn been jilted. If this happens, you will
believe that you feel sincere sympathy, but you will suddenly be
much more delighted than before with the beauties of tropical
islands or the wonders of Chinese art. A secondary desire,
derived from a false judgment as to a primary desire, has its own
power of influencing action, and is therefore a real desire
according to our definition. But it has not the same power as a
primary desire of bringing thorough satisfaction when it is
realized; so long as the primary desire remains unsatisfied,
restlessness continues in spite of the secondary desire's
success. Hence arises a belief in the vanity of human wishes: the
vain wishes are those that are secondary, but mistaken beliefs
prevent us from realizing that they are secondary.

What may, with some propriety, be called self-deception arises
through the operation of desires for beliefs. We desire many
things which it is not in our power to achieve: that we should be
universally popular and admired, that our work should be the
wonder of the age, and that the universe should be so ordered as
to bring ultimate happiness to all, though not to our enemies
until they have repented and been purified by suffering. Such
desires are too large to be achieved through our own efforts. But
it is found that a considerable portion of the satisfaction which
these things would bring us if they were realized is to be
achieved by the much easier operation of believing that they are
or will be realized. This desire for beliefs, as opposed to
desire for the actual facts, is a particular case of secondary
desire, and, like all secondary desire its satisfaction does not
lead to a complete cessation of the initial discomfort.
Nevertheless, desire for beliefs, as opposed to desire for facts,
is exceedingly potent both individually and socially. According
to the form of belief desired, it is called vanity, optimism, or
religion. Those who have sufficient power usually imprison or put
to death any one who tries to shake their faith in their own
excellence or in that of the universe; it is for this reason that
seditious libel and blasphemy have always been, and still are,
criminal offences.

It is very largely through desires for beliefs that the primitive
nature of desire has become so hidden, and that the part played
by consciousness has been so confusing and so exaggerated.

We may now summarize our analysis of desire and feeling.

A mental occurrence of any kind--sensation, image, belief, or
emotion--may be a cause of a series of actions, continuing,
unless interrupted, until some more or less definite state of
affairs is realized. Such a series of actions we call a
"behaviour-cycle." The degree of definiteness may vary greatly:
hunger requires only food in general, whereas the sight of a
particular piece of food raises a desire which requires the
eating of that piece of food. The property of causing such a
cycle of occurrences is called "discomfort"; the property of the
mental occurrences in which the cycle ends is called " pleasure."
The actions constituting the cycle must not be purely mechanical,
i.e. they must be bodily movements in whose causation the special
properties of nervous tissue are involved. The cycle ends in a
condition of quiescence, or of such action as tends only to
preserve the status quo. The state of affairs in which this
condition of quiescence is achieved is called the "purpose" of
the cycle, and the initial mental occurrence involving discomfort
is called a "desire" for the state of affairs that brings
quiescence. A desire is called "conscious" when it is accompanied
by a true belief as to the state of affairs that will bring
quiescence; otherwise it is called "unconscious." All primitive
desire is unconscious, and in human beings beliefs as to the
purposes of desires are often mistaken. These mistaken beliefs
generate secondary desires, which cause various interesting
complications in the psychology of human desire, without
fundamentally altering the character which it shares with animal


In this lecture we shall be concerned with a very general
characteristic which broadly, though not absolutely,
distinguishes the behaviour of living organisms from that of dead
matter. The characteristic in question is this:

The response of an organism to a given stimulus is very often
dependent upon the past history of the organism, and not merely
upon the stimulus and the HITHERTO DISCOVERABLE present state of
the organism.

This characteristic is embodied in the saying "a burnt child
fears the fire." The burn may have left no visible traces, yet it
modifies the reaction of the child in the presence of fire. It is
customary to assume that, in such cases, the past operates by
modifying the structure of the brain, not directly. I have no
wish to suggest that this hypothesis is false; I wish only to
point out that it is a hypothesis. At the end of the present
lecture I shall examine the grounds in its favour. If we confine
ourselves to facts which have been actually observed, we must say
that past occurrences, in addition to the present stimulus and
the present ascertainable condition of the organism, enter into
the causation of the response.

The characteristic is not wholly confined to living organisms.
For example, magnetized steel looks just like steel which has not
been magnetized, but its behaviour is in some ways different. In
the case of dead matter, however, such phenomena are less
frequent and important than in the case of living organisms, and
it is far less difficult to invent satisfactory hypotheses as to
the microscopic changes of structure which mediate between the
past occurrence and the present changed response. In the case of
living organisms, practically everything that is distinctive both
of their physical and of their mental behaviour is bound up with
this persistent influence of the past. Further, speaking broadly,
the change in response is usually of a kind that is biologically
advantageous to the organism.

Following a suggestion derived from Semon ("Die Mneme," Leipzig,
1904; 2nd edition, 1908, English translation, Allen & Unwin,
1921; "Die mnemischen Empfindungen," Leipzig, l909), we will give
the name of "mnemic phenomena" to those responses of an organism
which, so far as hitherto observed facts are concerned, can only
be brought under causal laws by including past occurrences in the
history of the organism as part of the causes of the present
response. I do not mean merely--what would always be the
case--that past occurrences are part of a CHAIN of causes leading
to the present event. I mean that, in attempting to state the
PROXIMATE cause of the present event, some past event or events
must be included, unless we take refuge in hypothetical
modifications of brain structure.) For example: you smell
peat-smoke, and you recall some occasion when you smelt it
before. The cause of your recollection, so far as hitherto observ
able phenomena are concerned, consists both of the peat smoke
(present stimulus) and of the former occasion (past experience).
The same stimulus will not produce the same recollection in
another man who did not share your former experience, although
the former experience left no OBSERVABLE traces in the structure
of the brain. According to the maxim "same cause, same effect,"
we cannot therefore regard the peat-smoke alone as the cause of
your recollection, since it does not have the same effect in
other cases. The cause of your recollection must be both the
peat-smoke and the past occurrence. Accordingly your recollection
is an instance of what we are calling "mnemic phenomena."

Before going further, it will be well to give illustrations of
different classes of mnemic phenomena.

(a) ACQUIRED HABITS.--In Lecture II we saw how animals can learn
by experience how to get out of cages or mazes, or perform other
actions which are useful to them but not provided for by their
instincts alone. A cat which is put into a cage of which it has
had experience behaves differently from the way in which it
behaved at first. We can easily invent hypotheses, which are
quite likely to be true, as to connections in the brain caused by
past experience, and themselves causing the different response.
But the observable fact is that the stimulus of being in the cage
produces differing results with repetition, and that the
ascertainable cause of the cat's behaviour is not merely the cage
and its own ascertainable organization, but also its past history
in regard to the cage. From our present point of view, the matter
is independent of the question whether the cat's behaviour is due
to some mental fact called "knowledge," or displays a merely
bodily habit. Our habitual knowledge is not always in our minds,
but is called up by the appropriate stimuli. If we are asked
"What is the capital of France?" we answer "Paris," because of
past experience; the past experience is as essential as the
present question in the causation of our response. Thus all our
habitual knowledge consists of acquired habits, and comes under
the head of mnemic phenomena.

(b) IMAGES.--I shall have much to say about images in a later
lecture; for the present I am merely concerned with them in so
far as they are "copies" of past sensations. When you hear New
York spoken of, some image probably comes into your mind, either
of the place itself (if you have been there), or of some picture
of it (if you have not). The image is due to your past
experience, as well as to the present stimulus of the words "New
York." Similarly, the images you have in dreams are all dependent
upon your past experience, as well as upon the present stimulus
to dreaming. It is generally believed that all images, in their
simpler parts, are copies of sensations; if so, their mnemic
character is evident. This is important, not only on its own
account, but also because, as we shall see later, images play an
essential part in what is called "thinking."

(c) ASSOCIATION.--The broad fact of association, on the mental
side, is that when we experience something which we have
experienced before, it tends to call up the context of the former
experience. The smell of peat-smoke recalling a former scene is
an instance which we discussed a moment ago. This is obviously a
mnemic phenomenon. There is also a more purely physical
association, which is indistinguishable from physical habit. This
is the kind studied by Mr. Thorndike in animals, where a certain
stimulus is associated with a certain act. This is the sort which
is taught to soldiers in drilling, for example. In such a case
there need not be anything mental, but merely a habit of the
body. There is no essential distinction between association and
habit, and the observations which we made concerning habit as a
mnemic phenomenon are equally applicable to association.

object of a familiar kind, much of what appears subjectively to
be immediately given is really derived from past experience. When
we see an object, say a penny, we seem to be aware of its "real"
shape we have the impression of something circular, not of
something elliptical. In learning to draw, it is necessary to
acquire the art of representing things according to the
sensation, not according to the perception. And the visual
appearance is filled out with feeling of what the object would be
like to touch, and so on. This filling out and supplying of the
"real" shape and so on consists of the most usual correlates of
the sensational core in our perception. It may happen that, in
the particular case, the real correlates are unusual; for
example, if what we are seeing is a carpet made to look like
tiles. If so, the non-sensational part of our perception will be
illusory, i.e. it will supply qualities which the object in
question does not in fact have. But as a rule objects do have the
qualities added by perception, which is to be expected, since
experience of what is usual is the cause of the addition. If our
experience had been different, we should not fill out sensation
in the same way, except in so far as the filling out is
instinctive, not acquired. It would seem that, in man, all that
makes up space perception, including the correlation of sight and
touch and so on, is almost entirely acquired. In that case there
is a large mnemic element in all the common perceptions by means
of which we handle common objects. And, to take another kind of
instance, imagine what our astonishment would be if we were to
hear a cat bark or a dog mew. This emotion would be dependent
upon past experience, and would therefore be a mnemic phenomenon
according to the definition.

(e) MEMORY AS KNOWLEDGE.--The kind of memory of which I am now
speaking is definite knowledge of some past event in one's own
experience. From time to time we remember things that have
happened to us, because something in the present reminds us of
them. Exactly the same present fact would not call up the same
memory if our past experience had been different. Thus our
remembering is caused by--

(1) The present stimulus,

(2) The past occurrence.

It is therefore a mnemic phenomenon according to our definition.
A definition of "mnemic phenomena" which did not include memory
would, of course, be a bad one. The point of the definition is
not that it includes memory, but that it includes it as one of a
class of phenomena which embrace all that is characteristic in
the subject matter of psychology.

(f) EXPERIENCE.--The word "experience" is often used very
vaguely. James, as we saw, uses it to cover the whole primal
stuff of the world, but this usage seems objection able, since,
in a purely physical world, things would happen without there
being any experience. It is only mnemic phenomena that embody
experience. We may say that an animal "experiences" an occurrence
when this occurrence modifies the animal's subsequent behaviour,
i.e. when it is the mnemic portion of the cause of future
occurrences in the animal's life. The burnt child that fears the
fire has "experienced" the fire, whereas a stick that has been
thrown on and taken off again has not "experienced" anything,
since it offers no more resistance than before to being thrown
on. The essence of "experience" is the modification of behaviour
produced by what is experienced. We might, in fact, define one
chain of experience, or one biography, as a series of occurrences
linked by mnemic causation. I think it is this characteristic,
more than any other, that distinguishes sciences dealing with
living organisms from physics.

The best writer on mnemic phenomena known to me is Richard Semon,
the fundamental part of whose theory I shall endeavour to
summarize before going further:

When an organism, either animal or plant, is subjected to a
stimulus, producing in it some state of excitement, the removal
of the stimulus allows it to return to a condition of
equilibrium. But the new state of equilibrium is different from
the old, as may be seen by the changed capacity for reaction. The
state of equilibrium before the stimulus may be called the
"primary indifference-state"; that after the cessation of the
stimulus, the "secondary indifference-state." We define the
"engraphic effect" of a stimulus as the effect in making a
difference between the primary and secondary indifference-states,
and this difference itself we define as the "engram" due to the
stimulus. "Mnemic phenomena" are defined as those due to engrams;
in animals, they are specially associated with the nervous
system, but not exclusively, even in man.

When two stimuli occur together, one of them, occurring
afterwards, may call out the reaction for the other also. We call
this an "ekphoric influence," and stimuli having this character
are called "ekphoric stimuli." In such a case we call the engrams
of the two stimuli "associated." All simultaneously generated
engrams are associated; there is also association of successively
aroused engrams, though this is reducible to simultaneous
association. In fact, it is not an isolated stimulus that leaves
an engram, but the totality of the stimuli at any moment;
consequently any portion of this totality tends, if it recurs, to
arouse the whole reaction which was aroused before. Semon holds
that engrams can be inherited, and that an animal's innate habits
may be due to the experience of its ancestors; on this subject he
refers to Samuel Butler.

Semon formulates two "mnemic principles." The first, or "Law of
Engraphy," is as follows: "All simultaneous excitements in an
organism form a connected simultaneous excitement-complex, which
as such works engraphically, i.e. leaves behind a connected
engram-complex, which in so far forms a whole" ("Die mnemischen
Empfindungen," p. 146). The second mnemic principle, or "Law of
Ekphory," is as follows: "The partial return of the energetic
situation which formerly worked engraphically operates
ekphorically on a simultaneous engram-complex" (ib., p. 173).
These two laws together represent in part a hypothesis (the
engram), and in part an observable fact. The observable fact is
that, when a certain complex of stimuli has originally caused a
certain complex of reactions, the recurrence of part of the
stimuli tends to cause the recurrence of the whole of the

Semon's applications of his fundamental ideas in various
directions are interesting and ingenious. Some of them will
concern us later, but for the present it is the fundamental
character of mnemic phenomena that is in question.

Concerning the nature of an engram, Semon confesses that at
present it is impossible to say more than that it must consist in
some material alteration in the body of the organism ("Die
mnemischen Empfindungen," p. 376). It is, in fact, hypothetical,
invoked for theoretical uses, and not an outcome of direct
observation. No doubt physiology, especially the disturbances of
memory through lesions in the brain, affords grounds for this
hypothesis; nevertheless it does remain a hypothesis, the
validity of which will be discussed at the end of this lecture.

I am inclined to think that, in the present state of physiology,
the introduction of the engram does not serve to simplify the
account of mnemic phenomena. We can, I think, formulate the known
laws of such phenomena in terms, wholly, of observable facts, by
recognizing provisionally what we may call "mnemic causation." By
this I mean that kind of causation of which I spoke at the
beginning of this lecture, that kind, namely, in which the
proximate cause consists not merely of a present event, but of
this together with a past event. I do not wish to urge that this
form of causation is ultimate, but that, in the present state of
our knowledge, it affords a simplification, and enables us to
state laws of behaviour in less hypothetical terms than we should
otherwise have to employ.

The clearest instance of what I mean is recollection of a past
event. What we observe is that certain present stimuli lead us to
recollect certain occurrences, but that at times when we are not
recollecting them, there is nothing discoverable in our minds
that could be called memory of them. Memories, as mental facts,
arise from time to time, but do not, so far as we can see, exist
in any shape while they are "latent." In fact, when we say that
they are "latent," we mean merely that they will exist under
certain circumstances. If, then, there is to be some standing
difference between the person who can remember a certain fact and
the person who cannot, that standing difference must be, not in
anything mental, but in the brain. It is quite probable that
there is such a difference in the brain, but its nature is
unknown and it remains hypothetical. Everything that has, so far,
been made matter of observation as regards this question can be
put together in the statement: When a certain complex of
sensations has occurred to a man, the recurrence of part of the
complex tends to arouse the recollection of the whole. In like
manner, we can collect all mnemic phenomena in living organisms
under a single law, which contains what is hitherto verifiable in
Semon's two laws. This single law is:


This law would need to be supplemented by some account of the
influence of frequency, and so on; but it seems to contain the
essential characteristic of mnemic phenomena, without admixture
of anything hypothetical.

Whenever the effect resulting from a stimulus to an organism
differs according to the past history of the organism, without
our being able actually to detect any relevant difference in its
present structure, we will speak of "mnemic causation," provided
we can discover laws embodying the influence of the past. In
ordinary physical causation, as it appears to common sense, we
have approximate uniformities of sequence, such as "lightning is
followed by thunder," "drunkenness is followed by headache," and
so on. None of these sequences are theoretically invariable,
since something may intervene to disturb them. In order to obtain
invariable physical laws, we have to proceed to differential
equations, showing the direction of change at each moment, not
the integral change after a finite interval, however short. But
for the purposes of daily life many sequences are to all in tents
and purposes invariable. With the behaviour of human beings,
however, this is by no means the case. If you say to an
Englishman, "You have a smut on your nose," he will proceed to
remove it, but there will be no such effect if you say the same
thing to a Frenchman who knows no English. The effect of words
upon the hearer is a mnemic phenomena, since it depends upon the
past experience which gave him understanding of the words. If
there are to be purely psychological causal laws, taking no
account of the brain and the rest of the body, they will have to
be of the form, not "X now causes Y now," but--

"A, B, C, . . . in the past, together with X now, cause Y now."
For it cannot be successfully maintained that our understanding
of a word, for example, is an actual existent content of the mind
at times when we are not thinking of the word. It is merely what
may be called a "disposition," i.e. it is capable of being
aroused whenever we hear the word or happen to think of it. A
"disposition" is not something actual, but merely the mnemic
portion of a mnemic causal law.

In such a law as "A, B, C, . . . in the past, together with X
now, cause Y now," we will call A, B, C, . . . the mnemic cause,
X the occasion or stimulus, and Y the reaction. All cases in
which experience influences behaviour are instances of mnemic

Believers in psycho-physical parallelism hold that psychology can
theoretically be freed entirely from all dependence on physiology
or physics. That is to say, they believe that every psychical
event has a psychical cause and a physical concomitant. If there
is to be parallelism, it is easy to prove by mathematical logic
that the causation in physical and psychical matters must be of
the same sort, and it is impossible that mnemic causation should
exist in psychology but not in physics. But if psychology is to
be independent of physiology, and if physiology can be reduced to
physics, it would seem that mnemic causation is essential in
psychology. Otherwise we shall be compelled to believe that all
our knowledge, all our store of images and memories, all our
mental habits, are at all times existing in some latent mental
form, and are not merely aroused by the stimuli which lead to
their display. This is a very difficult hypothesis. It seems to
me that if, as a matter of method rather than metaphysics, we
desire to obtain as much independence for psychology as is
practically feasible, we shall do better to accept mnemic
causation in psychology protem, and therefore reject parallelism,
since there is no good ground for admitting mnemic causation in

It is perhaps worth while to observe that mnemic causation is
what led Bergson to deny that there is causation. at all in the
psychical sphere. He points out, very truly, that the same
stimulus, repeated, does not have the same consequences, and he
argues that this is contrary to the maxim, "same cause, same
effect." It is only necessary, however, to take account of past
occurrences and include them with the cause, in order to
re-establish the maxim, and the possibility of psychological
causal laws. The metaphysical conception of a cause lingers in
our manner of viewing causal laws: we want to be able to FEEL a
connection between cause and effect, and to be able to imagine
the cause as "operating." This makes us unwilling to regard
causal laws as MERELY observed uniformities of sequence; yet that
is all that science has to offer. To ask why such-and-such a kind
of sequence occurs is either to ask a meaningless question, or to
demand some more general kind of sequence which includes the one
in question. The widest empirical laws of sequence known at any
time can only be "explained" in the sense of being subsumed by
later discoveries under wider laws; but these wider laws, until
they in turn are subsumed, will remain brute facts, resting
solely upon observation, not upon some supposed inherent

There is therefore no a priori objection to a causal law in which
part of the cause has ceased to exist. To argue against such a
law on the ground that what is past cannot operate now, is to
introduce the old metaphysical notion of cause, for which science
can find no place. The only reason that could be validly alleged
against mnemic causation would be that, in fact, all the
phenomena can be explained without it. They are explained without
it by Semon's "engram," or by any theory which regards the
results of experience as embodied in modifications of the brain
and nerves. But they are not explained, unless with extreme
artificiality, by any theory which regards the latent effects of
experience as psychical rather than physical. Those who desire to
make psychology as far as possible independent of physiology
would do well, it seems to me, if they adopted mnemic causation.
For my part, however, I have no such desire, and I shall
therefore endeavour to state the grounds which occur to me in
favour of some such view as that of the "engram."

One of the first points to be urged is that mnemic phenomena are
just as much to be found in physiology as in psychology. They are
even to be found in plants, as Sir Francis Darwin pointed out
(cf. Semon, "Die Mneme," 2nd edition, p. 28 n.). Habit is a
characteristic of the body at least as much as of the mind. We
should, therefore, be compelled to allow the intrusion of mnemic
causation, if admitted at all, into non-psychological regions,
which ought, one feels, to be subject only to causation of the
ordinary physical sort. The fact is that a great deal of what, at
first sight, distinguishes psychology from physics is found, on
examination, to be common to psychology and physiology; this
whole question of the influence of experience is a case in point.
Now it is possible, of course, to take the view advocated by
Professor J. S. Haldane, who contends that physiology is not
theoretically reducible to physics and chemistry.* But the weight
of opinion among physiologists appears to be against him on this
point; and we ought certainly to require very strong evidence
before admitting any such breach of continuity as between living
and dead matter. The argument from the existence of mnemic
phenomena in physiology must therefore be allowed a certain
weight against the hypothesis that mnemic causation is ultimate.

* See his "The New Physiology and Other Addresses," Griffin,
1919, also the symposium, "Are Physical, Biological and
Psychological Categories Irreducible?" in "Life and Finite
Individuality," edited for the Aristotelian Society, with an
Introduction. By H. Wildon Carr, Williams & Norgate, 1918.

The argument from the connection of brain-lesions with loss of
memory is not so strong as it looks, though it has also, some
weight. What we know is that memory, and mnemic phenomena
generally, can be disturbed or destroyed by changes in the brain.
This certainly proves that the brain plays an essential part in
the causation of memory, but does not prove that a certain state
of the brain is, by itself, a sufficient condition for the
existence of memory. Yet it is this last that has to be proved.
The theory of the engram, or any similar theory, has to maintain
that, given a body and brain in a suitable state, a man will have
a certain memory, without the need of any further conditions.
What is known, however, is only that he will not have memories if
his body and brain are not in a suitable state. That is to say,
the appropriate state of body and brain is proved to be necessary
for memory, but not to be sufficient. So far, therefore, as our
definite knowledge goes, memory may require for its causation a
past occurrence as well as a certain present state of the brain.

In order to prove conclusively that mnemic phenomena arise
whenever certain physiological conditions are fulfilled, we ought
to be able actually to see differences between the brain of a man
who speaks English and that of a man who speaks French, between
the brain of a man who has seen New York and can recall it, and
that of a man who has never seen that city. It may be that the
time will come when this will be possible, but at present we are
very far removed from it. At present, there is, so far as I am
aware, no good evidence that every difference between the
knowledge possessed by A and that possessed by B is paralleled by
some difference in their brains. We may believe that this is the
case, but if we do, our belief is based upon analogies and
general scientific maxims, not upon any foundation of detailed
observation. I am myself inclined, as a working hypothesis, to
adopt the belief in question, and to hold that past experience
only affects present behaviour through modifications of
physiological structure. But the evidence seems not quite
conclusive, so that I do not think we ought to forget the other
hypothesis, or to reject entirely the possibility that mnemic
causation may be the ultimate explanation of mnemic phenomena. I
say this, not because I think it LIKELY that mnemic causation is
ultimate, but merely because I think it POSSIBLE, and because it
often turns out important to the progress of science to remember
hypotheses which have previously seemed improbable.


The traditional conception of cause and effect is one which
modern science shows to be fundamentally erroneous, and requiring
to be replaced by a quite different notion, that of LAWS OF
CHANGE. In the traditional conception, a particular event A
caused a particular event B, and by this it was implied that,
given any event B, some earlier event A could be discovered which
had a relation to it, such that--

(1) Whenever A occurred, it was followed by B;

(2) In this sequence, there was something "necessary," not a mere
de facto occurrence of A first and then B.

The second point is illustrated by the old discussion as to
whether it can be said that day causes night, on the ground that
day is always followed by night. The orthodox answer was that day
could not be called the cause of night, because it would not be
followed by night if the earth's rotation were to cease, or
rather to grow so slow that one complete rotation would take a
year. A cause, it was held, must be such that under no
conceivable circumstances could it fail to be followed by its

As a matter of fact, such sequences as were sought by believers
in the traditional form of causation have not so far been found
in nature. Everything in nature is apparently in a state of
continuous change,* so that what we call one "event" turns out to
be really a process. If this event is to cause another event, the
two will have to be contiguous in time; for if there is any
interval between them, something may happen during that interval
to prevent the expected effect. Cause and effect, therefore, will
have to be temporally contiguous processes. It is difficult to
believe, at any rate where physical laws are concerned, that the
earlier part of the process which is the cause can make any
difference to the effect, so long as the later part of the
process which is the cause remains unchanged. Suppose, for
example, that a man dies of arsenic poisoning, we say that his
taking arsenic was the cause of death. But clearly the process by
which he acquired the arsenic is irrelevant: everything that
happened before he swallowed it may be ignored, since it cannot
alter the effect except in so far as it alters his condition at
the moment of taking the dose. But we may go further: swallowing
arsenic is not really the proximate cause of death, since a man
might be shot through the head immediately after taking the dose,
and then it would not be of arsenic that he would die. The
arsenic produces certain physiological changes, which take a
finite time before they end in death. The earlier parts of these
changes can be ruled out in the same way as we can rule out the
process by which the arsenic was acquired. Proceeding in this
way, we can shorten the process which we are calling the cause
more and more. Similarly we shall have to shorten the effect. It
may happen that immediately after the man's death his body is
blown to pieces by a bomb. We cannot say what will happen after
the man's death, through merely knowing that he has died as the
result of arsenic poisoning. Thus, if we are to take the cause as
one event and the effect as another, both must be shortened
indefinitely. The result is that we merely have, as the
embodiment of our causal law, a certain direction of change at
each moment. Hence we are brought to differential equations as
embodying causal laws. A physical law does not say "A will be
followed by B," but tells us what acceleration a particle will
have under given circumstances, i.e. it tells us how the
particle's motion is changing at each moment, not where the
particle will be at some future moment.

* The theory of quanta suggests that the continuity is only
apparent. If so, we shall be able theoretically to reach events
which are not processes. But in what is directly observable there
is still apparent continuity, which justifies the above remarks
for the prevent.

Laws embodied in differential equations may possibly be exact,
but cannot be known to be so. All that we can know empirically is
approximate and liable to exceptions; the exact laws that are
assumed in physics are known to be somewhere near the truth, but
are not known to be true just as they stand. The laws that we
actually know empirically have the form of the traditional causal
laws, except that they are not to be regarded as universal or
necessary. "Taking arsenic is followed by death" is a good
empirical generalization; it may have exceptions, but they will
be rare. As against the professedly exact laws of physics, such
empirical generalizations have the advantage that they deal with
observable phenomena. We cannot observe infinitesimals, whether
in time or space; we do not even know whether time and space are
infinitely divisible. Therefore rough empirical generalizations
have a definite place in science, in spite of not being exact of
universal. They are the data for more exact laws, and the grounds
for believing that they are USUALLY true are stronger than the
grounds for believing that the more exact laws are ALWAYS true.

Science starts, therefore, from generalizations of the form, "A
is usually followed by B." This is the nearest approach that can
be made to a causal law of the traditional sort. It may happen in
any particular instance that A is ALWAYS followed by B, but we
cannot know this, since we cannot foresee all the perfectly
possible circumstances that might make the sequence fail, or know
that none of them will actually occur. If, however, we know of a
very large number of cases in which A is followed by B, and few
or none in which the sequence fails, we shall in PRACTICE be
justified in saying "A causes B," provided we do not attach to
the notion of cause any of the metaphysical superstitions that
have gathered about the word.

There is another point, besides lack of universality and
necessity, which it is important to realize as regards causes in
the above sense, and that is the lack of uniqueness. It is
generally assumed that, given any event, there is some one
phenomenon which is THE cause of the event in question. This
seems to be a mere mistake. Cause, in the only sense in which it
can be practically applied, means "nearly invariable antecedent."
We cannot in practice obtain an antecedent which is QUITE
invariable, for this would require us to take account of the
whole universe, since something not taken account of may prevent
the expected effect. We cannot distinguish, among nearly
invariable antecedents, one as THE cause, and the others as
merely its concomitants: the attempt to do this depends upon a
notion of cause which is derived from will, and will (as we shall
see later) is not at all the sort of thing that it is generally
supposed to be, nor is there any reason to think that in the
physical world there is anything even remotely analogous to what
will is supposed to be. If we could find one antecedent, and only
one, that was QUITE invariable, we could call that one THE cause
without introducing any notion derived from mistaken ideas about
will. But in fact we cannot find any antecedent that we know to
be quite invariable, and we can find many that are nearly so. For
example, men leave a factory for dinner when the hooter sounds at
twelve o'clock. You may say the hooter is THE cause of their
leaving. But innumerable other hooters in other factories, which
also always sound at twelve o'clock, have just as good a right to
be called the cause. Thus every event has many nearly invariable
antecedents, and therefore many antecedents which may be called
its cause.

The laws of traditional physics, in the form in which they deal
with movements of matter or electricity, have an apparent
simplicity which somewhat conceals the empirical character of
what they assert. A piece of matter, as it is known empirically,
is not a single existing thing, but a system of existing things.
When several people simultaneously see the same table, they all
see something different; therefore "the" table, which they are
supposed all to see, must be either a hypothesis or a
construction. "The" table is to be neutral as between different
observers: it does not favour the aspect seen by one man at the
expense of that seen by another. It was natural, though to my
mind mistaken, to regard the "real" table as the common cause of
all the appearances which the table presents (as we say) to
different observers. But why should we suppose that there is some
one common cause of all these appearances? As we have just seen,
the notion of "cause" is not so reliable as to allow us to infer
the existence of something that, by its very nature, can never be

Instead of looking for an impartial source, we can secure
neutrality by the equal representation of all parties. Instead of
supposing that there is some unknown cause, the "real" table,
behind the different sensations of those who are said to be
looking at the table, we may take the whole set of these
sensations (together possibly with certain other particulars) as
actually BEING the table. That is to say, the table which is
neutral as between different observers (actual and possible) is
the set of all those particulars which would naturally be called
"aspects" of the table from different points of view. (This is a
first approximation, modified later.)

It may be said: If there is no single existent which is the
source of all these "aspects," how are they collected together?
The answer is simple: Just as they would be if there were such a
single existent. The supposed "real" table underlying its
appearances is, in any case, not itself perceived, but inferred,
and the question whether such-and-such a particular is an
"aspect" of this table is only to be settled by the connection of
the particular in question with the one or more particulars by
which the table is defined. That is to say, even if we assume a
"real" table, the particulars which are its aspects have to be
collected together by their relations to each other, not to it,
since it is merely inferred from them. We have only, therefore,
to notice how they are collected together, and we can then keep
the collection without assuming any "real" table as distinct from
the collection. When different people see what they call the same
table, they see things which are not exactly the same, owing to
difference of point of view, but which are sufficiently alike to
be described in the same words, so long as no great accuracy or
minuteness is sought. These closely similar particulars are
collected together by their similarity primarily and, more
correctly, by the fact that they are related to each other
approximately according to the laws of perspective and of
reflection and diffraction of light. I suggest, as a first
approximation, that these particulars, together with such
correlated others as are unperceived, jointly ARE the table; and
that a similar definition applies to all physical objects.*

*See "Our Knowledge of the External World" (Allen & Unwin),
chaps. iii and iv.

In order to eliminate the reference to our perceptions, which
introduces an irrelevant psychological suggestion, I will take a
different illustration, namely, stellar photography. A
photographic plate exposed on a clear night reproduces the
appearance of the portion of the sky concerned, with more or
fewer stars according to the power of the telescope that is being
used. Each separate star which is photographed produces its
separate effect on the plate, just as it would upon ourselves if
we were looking at the sky. If we assume, as science normally
does, the continuity of physical processes, we are forced to
conclude that, at the place where the plate is, and at all places
between it and a star which it photographs, SOMETHING is
happening which is specially connected with that star. In the
days when the aether was less in doubt, we should have said that
what was happening was a certain kind of transverse vibration in
the aether. But it is not necessary or desirable to be so
explicit: all that we need say is that SOMETHING happens which is
specially connected with the star in question. It must be
something specially connected with that star, since that star
produces its own special effect upon the plate. Whatever it is
must be the end of a process which starts from the star and
radiates outwards, partly on general grounds of continuity,
partly to account for the fact that light is transmitted with a
certain definite velocity. We thus arrive at the conclusion that,
if a certain star is visible at a certain place, or could be
photographed by a sufficiently sensitive plate at that place,
something is happening there which is specially connected with
that star. Therefore in every place at all times a vast multitude
of things must be happening, namely, at least one for every
physical object which can be seen or photographed from that
place. We can classify such happenings on either of two

(1) We can collect together all the happenings in one place, as
is done by photography so far as light is concerned;

(2) We can collect together all the happenings, in different
places, which are connected in the way that common sense regards
as being due to their emanating from one object.

Thus, to return to the stars, we can collect together either--

(1) All the appearances of different stars in a given place, or,

(2) All the appearances of a given star in different places.

But when I speak of "appearances," I do so only for brevity: I do
not mean anything that must "appear" to somebody, but only that
happening, whatever it may be, which is connected, at the place
in question, with a given physical object--according to the old
orthodox theory, it would be a transverse vibration in the
aether. Like the different appearances of the table to a number
of simultaneous observers, the different particulars that belong
to one physical object are to be collected together by continuity
and inherent laws of correlation, not by their supposed causal
connection with an unknown assumed existent called a piece of
matter, which would be a mere unnecessary metaphysical thing in
itself. A piece of matter, according to the definition that I
propose, is, as a first approximation,* the collection of all
those correlated particulars which would normally be regarded as
its appearances or effects in different places. Some further
elaborations are desirable, but we can ignore them for the
present. I shall return to them at the end of this lecture.

*The exact definition of a piece of matter as a construction will
be given later.

According to the view that I am suggesting, a physical object or
piece of matter is the collection of all those correlated
particulars which would be regarded by common sense as its
effects or appearances in different places. On the other hand,
all the happenings in a given place represent what common sense
would regard as the appearances of a number of different objects
as viewed from that place. All the happenings in one place may be
regarded as the view of the world from that place. I shall call
the view of the world from a given place a "perspective." A
photograph represents a perspective. On the other hand, if
photographs of the stars were taken in all points throughout
space, and in all such photographs a certain star, say Sirius,
were picked out whenever it appeared, all the different
appearances of Sirius, taken together, would represent Sirius.
For the understanding of the difference between psychology and
physics it is vital to understand these two ways of classifying
particulars, namely:

(1) According to the place where they occur;

(2) According to the system of correlated particulars in
different places to which they belong, such system being defined
as a physical object.

Given a system of particulars which is a physical object, I shall
define that one of the system which is in a given place (if any)
as the "appearance of that object in that place."

When the appearance of an object in a given place changes, it is
found that one or other of two things occurs. The two
possibilities may be illustrated by an example. You are in a room
with a man, whom you see: you may cease to see him either by
shutting your eyes or by his going out of the room. In the first
case, his appearance to other people remains unchanged; in the
second, his appearance changes from all places. In the first
case, you say that it is not he who has changed, but your eyes;
in the second, you say that he has changed. Generalizing, we

(1) Cases in which only certain appearances of the object change,
while others, and especially appearances from places very near to
the object, do not change;

(2) Cases where all, or almost all, the appearances of the object
undergo a connected change.

In the first case, the change is attributed to the medium between
the object and the place; in the second, it is attributed to the
object itself.*

* The application of this distinction to motion raises
complications due to relativity, but we may ignore these for our
present purposes.

It is the frequency of the latter kind of change, and the
comparatively simple nature of the laws governing the
simultaneous alterations of appearances in such cases, that have
made it possible to treat a physical object as one thing, and to
overlook the fact that it is a system of particulars. When a
number of people at a theatre watch an actor, the changes in
their several perspectives are so similar and so closely
correlated that all are popularly regarded as identical with each
other and with the changes of the actor himself. So long as all
the changes in the appearances of a body are thus correlated
there is no pressing prima facie need to break up the system of
appearances, or to realize that the body in question is not
really one thing but a set of correlated particulars. It is
especially and primarily such changes that physics deals with,
i.e. it deals primarily with processes in which the unity of a
physical object need not be broken up because all its appearances
change simultaneously according to the same law--or, if not all,
at any rate all from places sufficiently near to the object, with
in creasing accuracy as we approach the object.

The changes in appearances of an object which are due to changes
in the intervening medium will not affect, or will affect only
very slightly, the appearances from places close to the object.
If the appearances from sufficiently neighbouring places are
either wholly un changed, or changed to a diminishing extent
which has zero for its limit, it is usually found that the
changes can be accounted for by changes in objects which are
between the object in question and the places from which its
appearance has changed appreciably. Thus physics is able to
reduce the laws of most changes with which it deals to changes in
physical objects, and to state most of its fundamental laws in
terms of matter. It is only in those cases in which the unity of
the system of appearances constituting a piece of matter has to
be broken up, that the statement of what is happening cannot be
made exclusively in terms of matter. The whole of psychology, we
shall find, is included among such cases; hence their importance
for our purposes.

We can now begin to understand one of the fundamental differences
between physics and psychology. Physics treats as a unit the
whole system of appearances of a piece of matter, whereas
psychology is interested in certain of these appearances
themselves. Confining ourselves for the moment to the psychology
of perceptions, we observe that perceptions are certain of the
appearances of physical objects. From the point of view that we
have been hitherto adopting, we might define them as the
appearances of objects at places from which sense-organs and the
suitable parts of the nervous system form part of the intervening
medium. Just as a photographic plate receives a different
impression of a cluster of stars when a telescope is part of the
intervening medium, so a brain receives a different impression
when an eye and an optic nerve are part of the intervening
medium. An impression due to this sort of intervening medium is
called a perception, and is interesting to psychology on its own
account, not merely as one of the set of correlated particulars
which is the physical object of which (as we say) we are having a

We spoke earlier of two ways of classifying particulars. One way
collects together the appearances commonly regarded as a given
object from different places; this is, broadly speaking, the way
of physics, leading to the construction of physical objects as
sets of such appearances. The other way collects together the
appearances of different objects from a given place, the result
being what we call a perspective. In the particular case where
the place concerned is a human brain, the perspective belonging
to the place consists of all the perceptions of a certain man at
a given time. Thus classification by perspectives is relevant to
psychology, and is essential in defining what we mean by one

I do not wish to suggest that the way in which I have been
defining perceptions is the only possible way, or even the best
way. It is the way that arose naturally out of our present topic.
But when we approach psychology from a more introspective
standpoint, we have to distinguish sensations and perceptions, if
possible, from other mental occurrences, if any. We have also to
consider the psychological effects of sensations, as opposed to
their physical causes and correlates. These problems are quite
distinct from those with which we have been concerned in the
present lecture, and I shall not deal with them until a later

It is clear that psychology is concerned essentially with actual
particulars, not merely with systems of particulars. In this it
differs from physics, which, broadly speaking, is concerned with
the cases in which all the particulars which make up one physical
object can be treated as a single causal unit, or rather the
particulars which are sufficiently near to the object of which
they are appearances can be so treated. The laws which physics
seeks can, broadly speaking, be stated by treating such systems
of particulars as causal units. The laws which psychology seeks
cannot be so stated, since the particulars themselves are what
interests the psychologist. This is one of the fundamental
differences between physics and psychology; and to make it clear
has been the main purpose of this lecture.

I will conclude with an attempt to give a more precise definition
of a piece of matter. The appearances of a piece of matter from
different places change partly according to intrinsic laws (the
laws of perspective, in the case of visual shape), partly
according to the nature of the intervening medium--fog, blue
spectacles, telescopes, microscopes, sense-organs, etc. As we
approach nearer to the object, the effect of the intervening
medium grows less. In a generalized sense, all the intrinsic laws
of change of appearance may be called "laws of perspective."
Given any appearance of an object, we can construct
hypothetically a certain system of appearances to which the
appearance in question would belong if the laws of perspective
alone were concerned. If we construct this hypothetical system
for each appearance of the object in turn, the system
corresponding to a given appearance x will be independent of any
distortion due to the medium beyond x, and will only embody such
distortion as is due to the medium between x and the object.
Thus, as the appearance by which our hypothetical system is
defined is moved nearer and nearer to the object, the
hypothetical system of appearances defined by its means embodies
less and less of the effect of the medium. The different sets of
appearances resulting from moving x nearer and nearer to the
object will approach to a limiting set, and this limiting set
will be that system of appearances which the object would present
if the laws of perspective alone were operative and the medium
exercised no distorting effect. This limiting set of appearances
may be defined, for purposes of physics, as the piece of matter


One of the main purposes of these lectures is to give grounds for
the belief that the distinction between mind and matter is not so
fundamental as is commonly supposed. In the preceding lecture I
dealt in outline with the physical side of this problem. I
attempted to show that what we call a material object is not
itself a substance, but is a system of particulars analogous in
their nature to sensations, and in fact often including actual
sensations among their number. In this way the stuff of which
physical objects are composed is brought into relation with the
stuff of which part, at least, of our mental life is composed.

There is, however, a converse task which is equally necessary for
our thesis, and that is, to show that the stuff of our mental
life is devoid of many qualities which it is commonly supposed to
have, and is not possessed of any attributes which make it
incapable of forming part of the world of matter. In the present
lecture I shall begin the arguments for this view.

Corresponding to the supposed duality of matter and mind, there
are, in orthodox psychology, two ways of knowing what exists. One
of these, the way of sensation and external perception, is
supposed to furnish data for our knowledge of matter, the other,
called "introspection," is supposed to furnish data for knowledge
of our mental processes. To common sense, this distinction seems
clear and easy. When you see a friend coming along the street,
you acquire knowledge of an external, physical fact; when you
realize that you are glad to meet him, you acquire knowledge of a
mental fact. Your dreams and memories and thoughts, of which you
are often conscious, are mental facts, and the process by which
you become aware of them SEEMS to be different from sensation.
Kant calls it the "inner sense"; sometimes it is spoken of as
"consciousness of self"; but its commonest name in modern English
psychology is "introspection." It is this supposed method of
acquiring knowledge of our mental processes that I wish to
analyse and examine in this lecture.

I will state at the outset the view which I shall aim at
establishing. I believe that the stuff of our mental life, as
opposed to its relations and structure, consists wholly of
sensations and images. Sensations are connected with matter in
the way that I tried to explain in Lecture V, i.e. each is a
member of a system which is a certain physical object. Images,
though they USUALLY have certain characteristics, especially lack
of vividness, that distinguish them from sensations, are not
INVARIABLY so distinguished, and cannot therefore be defined by
these characteristics. Images, as opposed to sensations, can only
be defined by their different causation: they are caused by
association with a sensation, not by a stimulus external to the
nervous system--or perhaps one should say external to the brain,
where the higher animals are concerned. The occurrence of a
sensation or image does not in itself constitute knowledge but
any sensation or image may come to be known if the conditions are
suitable. When a sensation--like the hearing of a clap of
thunder--is normally correlated with closely similar sensations
in our neighbours, we regard it as giving knowledge of the
external world, since we regard the whole set of similar
sensations as due to a common external cause. But images and
bodily sensations are not so correlated. Bodily sensations can be
brought into a correlation by physiology, and thus take their
place ultimately among sources of knowledge of the physical
world. But images cannot be made to fit in with the simultaneous
sensations and images of others. Apart from their hypothetical
causes in the brain, they have a causal connection with physical
objects, through the fact that they are copies of past
sensations; but the physical objects with which they are thus
connected are in the past, not in the present. These images
remain private in a sense in which sensations are not. A
sensation SEEMS to give us knowledge of a present physical
object, while an image does not, except when it amounts to a
hallucination, and in this case the seeming is deceptive. Thus
the whole context of the two occurrences is different. But in
themselves they do not differ profoundly, and there is no reason
to invoke two different ways of knowing for the one and for the
other. Consequently introspection as a separate kind of knowledge

The criticism of introspection has been in the main the work of
American psychologists. I will begin by summarizing an article
which seems to me to afford a good specimen of their arguments,
namely, "The Case against Introspection," by Knight Dunlap
("Psychological Review," vol xix, No. 5, pp. 404-413, September,
1912). After a few historical quotations, he comes to two modern
defenders of introspection, Stout and James. He quotes from Stout
such statements as the following: "Psychical states as such
become objects only when we attend to them in an introspective
way. Otherwise they are not themselves objects, but only
constituents of the process by which objects are recognized"
("Manual," 2nd edition, p. 134. The word "recognized" in Dunlap's
quotation should be "cognized.") "The object itself can never be
identified with the present modification of the individual's
consciousness by which it is cognized" (ib. p. 60). This is to be
true even when we are thinking about modifications of our own
consciousness; such modifications are to be always at least
partially distinct from the conscious experience in which we
think of them.

At this point I wish to interrupt the account of Knight Dunlap's
article in order to make some observations on my own account with
reference to the above quotations from Stout. In the first place,
the conception of "psychical states" seems to me one which
demands analysis of a somewhat destructive character. This
analysis I shall give in later lectures as regards cognition; I
have already given it as regards desire. In the second place, the
conception of "objects" depends upon a certain view as to
cognition which I believe to be wholly mistaken, namely, the view
which I discussed in my first lecture in connection with
Brentano. In this view a single cognitive occurrence contains
both content and object, the content being essentially mental,
while the object is physical except in introspection and abstract
thought. I have already criticized this view, and will not dwell
upon it now, beyond saying that "the process by which objects are
cognized" appears to be a very slippery phrase. When we "see a
table," as common sense would say, the table as a physical object
is not the "object" (in the psychological sense) of our
perception. Our perception is made up of sensations, images and
beliefs, but the supposed "object" is something inferential,
externally related, not logically bound up with what is occurring
in us. This question of the nature of the object also affects the
view we take of self-consciousness. Obviously, a "conscious
experience" is different from a physical object; therefore it is
natural to assume that a thought or perception whose object is a
conscious experience must be different from a thought or
perception whose object is a physical object. But if the relation
to the object is inferential and external, as I maintain, the
difference between two thoughts may bear very little relation to
the difference between their objects. And to speak of "the
present modification of the individual's consciousness by which
an object is cognized" is to suggest that the cognition of
objects is a far more direct process, far more intimately bound
up with the objects, than I believe it to be. All these points
will be amplified when we come to the analysis of knowledge, but
it is necessary briefly to state them now in order to suggest the
atmosphere in which our analysis of "introspection" is to be
carried on.

Another point in which Stout's remarks seem to me to suggest what
I regard as mistakes is his use of "consciousness." There is a
view which is prevalent among psychologists, to the effect that
one can speak of "a conscious experience" in a curious dual
sense, meaning, on the one hand, an experience which is conscious
of something, and, on the other hand, an experience which has
some intrinsic nature characteristic of what is called
"consciousness." That is to say, a "conscious experience" is
characterized on the one hand by relation to its object and on
the other hand by being composed of a certain peculiar stuff, the
stuff of "consciousness." And in many authors there is yet a
third confusion: a "conscious experience," in this third sense,
is an experience of which we are conscious. All these, it seems
to me, need to be clearly separated. To say that one occurrence
is "conscious" of another is, to my mind, to assert an external
and rather remote relation between them. I might illustrate it by
the relation of uncle and nephew a man becomes an uncle through
no effort of his own, merely through an occurrence elsewhere.
Similarly, when you are said to be "conscious" of a table, the
question whether this is really the case cannot be decided by
examining only your state of mind: it is necessary also to
ascertain whether your sensation is having those correlates which
past experience causes you to assume, or whether the table
happens, in this case, to be a mirage. And, as I explained in my
first lecture, I do not believe that there is any "stuff" of
consciousness, so that there is no intrinsic character by which a
"conscious" experience could be distinguished from any other.

After these preliminaries, we can return to Knight Dunlap's
article. His criticism of Stout turns on the difficulty of giving
any empirical meaning to such notions as the "mind" or the
"subject"; he quotes from Stout the sentence: "The most important
drawback is that the mind, in watching its own workings, must
necessarily have its attention divided between two objects," and
he concludes: "Without question, Stout is bringing in here
illicitly the concept of a single observer, and his introspection
does not provide for the observation of this observer; for the
process observed and the observer are distinct" (p. 407). The
objections to any theory which brings in the single observer were
considered in Lecture I, and were acknowledged to be cogent. In
so far, therefore, as Stout's theory of introspection rests upon
this assumption, we are compelled to reject it. But it is
perfectly possible to believe in introspection without supposing
that there is a single observer.

William James's theory of introspection, which Dunlap next
examines, does not assume a single observer. It changed after the
publication of his "Psychology," in consequence of his abandoning
the dualism of thought and things. Dunlap summarizes his theory
as follows:

"The essential points in James's scheme of consciousness are
SUBJECT, OBJECT,and a KNOWING of the object by the subject. The
difference between James's scheme and other schemes involving the
same terms is that James considers subject and object to be the
same thing, but at different times In order to satisfy this
requirement James supposes a realm of existence which he at first
called 'states of consciousness' or 'thoughts,' and later, 'pure
experience,' the latter term including both the 'thoughts' and
the 'knowing.' This scheme, with all its magnificent
artificiality, James held on to until the end, simply dropping
the term consciousness and the dualism between the thought and an
external reality"(p. 409).

He adds: "All that James's system really amounts to is the
acknowledgment that a succession of things are known, and that
they are known by something. This is all any one can claim,
except for the fact that the things are known together, and that
the knower for the different items is one and the same" (ib.).

In this statement, to my mind, Dunlap concedes far more than
James did in his later theory. I see no reason to suppose that
"the knower for different items is one and the same," and I am
convinced that this proposition could not possibly be ascertained
except by introspection of the sort that Dunlap rejects. The
first of these points must wait until we come to the analysis of
belief: the second must be considered now. Dunlap's view is that
there is a dualism of subject and object, but that the subject
can never become object, and therefore there is no awareness of
an awareness. He says in discussing the view that introspection
reveals the occurrence of knowledge: "There can be no denial of
the existence of the thing (knowing) which is alleged to be known
or observed in this sort of 'introspection.' The allegation that
the knowing is observed is that which may be denied. Knowing
there certainly is; known, the knowing certainly is not"(p. 410).
And again: "I am never aware of an awareness" (ib.). And on the
next page: "It may sound paradoxical to say that one cannot
observe the process (or relation) of observation, and yet may be
certain that there is such a process: but there is really no
inconsistency in the saying. How do I know that there is
awareness? By being aware of something. There is no meaning in
the term 'awareness' which is not expressed in the statement 'I
am aware of a colour (or what-not).' "

But the paradox cannot be so lightly disposed of. The statement
"I am aware of a colour" is assumed by Knight Dunlap to be known
to be true, but he does not explain how it comes to be known. The
argument against him is not conclusive, since he may be able to
show some valid way of inferring our awareness. But he does not
suggest any such way. There is nothing odd in the hypothesis of
beings which are aware of objects, but not of their own
awareness; it is, indeed, highly probable that young children and
the higher animals are such beings. But such beings cannot make
the statement "I am aware of a colour," which WE can make. We
have, therefore, some knowledge which they lack. It is necessary
to Knight Dunlap's position to maintain that this additional
knowledge is purely inferential, but he makes no attempt to show
how the inference is possible. It may, of course, be possible,
but I cannot see how. To my mind the fact (which he admits) that
we know there is awareness, is ALL BUT decisive against his
theory, and in favour of the view that we can be aware of an

Dunlap asserts (to return to James) that the real ground for
James's original belief in introspection was his belief in two
sorts of objects, namely, thoughts and things. He suggests that
it was a mere inconsistency on James's part to adhere to
introspection after abandoning the dualism of thoughts and
things. I do not wholly agree with this view, but it is difficult
to disentangle the difference as to introspection from the
difference as to the nature of knowing. Dunlap suggests (p. 411)
that what is called introspection really consists of awareness of
"images," visceral sensations, and so on. This view, in essence,
seems to me sound. But then I hold that knowing itself consists
of such constituents suitably related, and that in being aware of
them we are sometimes being aware of instances of knowing. For
this reason, much as I agree with his view as to what are the
objects of which there is awareness, I cannot wholly agree with
his conclusion as to the impossibility of introspection.

The behaviourists have challenged introspection even more
vigorously than Knight Dunlap, and have gone so far as to deny
the existence of images. But I think that they have confused
various things which are very commonly confused, and that it is
necessary to make several distinctions before we can arrive at
what is true and what false in the criticism of introspection.

I wish to distinguish three distinct questions, any one of which
may be meant when we ask whether introspection is a source of
knowledge. The three questions are as follows:

(1) Can we observe anything about ourselves which we cannot
observe about other people, or is everything we can observe
PUBLIC, in the sense that another could also observe it if
suitably placed?

(2) Does everything that we can observe obey the laws of physics
and form part of the physical world, or can we observe certain
things that lie outside physics?

(3) Can we observe anything which differs in its intrinsic nature
from the constituents of the physical world, or is everything
that we can observe composed of elements intrinsically similar to
the constituents of what is called matter?

Any one of these three questions may be used to define
introspection. I should favour introspection in the sense of the
first question, i.e. I think that some of the things we observe
cannot, even theoretically, be observed by any one else. The
second question, tentatively and for the present, I should answer
in favour of introspection; I think that images, in the actual
condition of science, cannot be brought under the causal laws of
physics, though perhaps ultimately they may be. The third
question I should answer adversely to introspection I think that
observation shows us nothing that is not composed of sensations
and images, and that images differ from sensations in their
causal laws, not intrinsically. I shall deal with the three
questions successively.

ourselves, for the moment, to sensations, we find that there are
different degrees of publicity attaching to different sorts of
sensations. If you feel a toothache when the other people in the
room do not, you are in no way surprised; but if you hear a clap
of thunder when they do not, you begin to be alarmed as to your
mental condition. Sight and hearing are the most public of the
senses; smell only a trifle less so; touch, again, a trifle less,
since two people can only touch the same spot successively, not
simultaneously. Taste has a sort of semi-publicity, since people
seem to experience similar taste-sensations when they eat similar
foods; but the publicity is incomplete, since two people cannot
eat actually the same piece of food.

But when we pass on to bodily sensations--headache, toothache,
hunger, thirst, the feeling of fatigue, and so on--we get quite
away from publicity, into a region where other people can tell us
what they feel, but we cannot directly observe their feeling. As
a natural result of this state of affairs, it has come to be
thought that the public senses give us knowledge of the outer
world, while the private senses only give us knowledge as to our
own bodies. As regards privacy, all images, of whatever sort,
belong with the sensations which only give knowledge of our own
bodies, i.e. each is only observable by one observer. This is the
reason why images of sight and hearing are more obviously
different from sensations of sight and hearing than images of
bodily sensations are from bodily sensations; and that is why the
argument in favour of images is more conclusive in such cases as
sight and hearing than in such cases as inner speech.

The whole distinction of privacy and publicity, however, so long
as we confine ourselves to sensations, is one of degree, not of
kind. No two people, there is good empirical reason to think,
ever have exactly similar sensations related to the same physical
object at the same moment; on the other hand, even the most
private sensation has correlations which would theoretically
enable another observer to infer it.

That no sensation is ever completely public, results from
differences of point of view. Two people looking at the same
table do not get the same sensation, because of perspective and
the way the light falls. They get only correlated sensations. Two
people listening to the same sound do not hear exactly the same
thing, because one is nearer to the source of the sound than the
other, one has better hearing than the other, and so on. Thus
publicity in sensations consists, not in having PRECISELY similar
sensations, but in having more or less similar sensations
correlated according to ascertainable laws. The sensations which
strike us as public are those where the correlated sensations are
very similar and the correlations are very easy to discover. But
even the most private sensations have correlations with things
that others can observe. The dentist does not observe your ache,
but he can see the cavity which causes it, and could guess that
you are suffering even if you did not tell him. This fact,
however, cannot be used, as Watson would apparently wish, to
extrude from science observations which are private to one
observer, since it is by means of many such observations that
correlations are established, e.g. between toothaches and
cavities. Privacy, therefore does not by itself make a datum
unamenable to scientific treatment. On this point, the argument
against introspection must be rejected.

now to the second ground of objection to introspection, namely,
that its data do not obey the laws of physics. This, though less
emphasized, is, I think, an objection which is really more
strongly felt than the objection of privacy. And we obtain a
definition of introspection more in harmony with usage if we
define it as observation of data not subject to physical laws
than if we define it by means of privacy. No one would regard a
man as introspective because he was conscious of having a stomach
ache. Opponents of introspection do not mean to deny the obvious
fact that we can observe bodily sensations which others cannot
observe. For example, Knight Dunlap contends that images are
really muscular contractions,* and evidently regards our
awareness of muscular contractions as not coming under the head
of introspection. I think it will be found that the essential
characteristic of introspective data, in the sense which now
concerns us, has to do with LOCALIZATION: either they are not
localized at all, or they are localized, like visual images, in a
place already physically occupied by something which would be
inconsistent with them if they were regarded as part of the
physical world. If you have a visual image of your friend sitting
in a chair which in fact is empty, you cannot locate the image in
your body, because it is visual, nor (as a physical phenomenon)
in the chair, because the chair, as a physical object, is empty.
Thus it seems to follow that the physical world does not include
all that we are aware of, and that images, which are
introspective data, have to be regarded, for the present, as not
obeying the laws of physics; this is, I think, one of the chief
reasons why an attempt is made to reject them. I shall try to
show in Lecture VIII that the purely empirical reasons for
accepting images are overwhelming. But we cannot be nearly so
certain that they will not ultimately be brought under the laws
of physics. Even if this should happen, however, they would still
be distinguishable from sensations by their proximate causal
laws, as gases remain distinguishable from solids.

* "Psychological Review," 1916, "Thought-Content and Feeling," p.
59. See also ib., 1912, "The Nature of Perceived Relations,"
where he says: "'Introspection,' divested of its mythological
suggestion of the observing of consciousness, is really the
observation of bodily sensations (sensibles) and feelings
(feelables)"(p. 427 n.).

SENSATIONS? We come now to our third question concerning
introspection. It is commonly thought that by looking within we
can observe all sorts of things that are radically different from
the constituents of the physical world, e.g. thoughts, beliefs,
desires, pleasures, pains and emotions. The difference between
mind and matter is increased partly by emphasizing these supposed
introspective data, partly by the supposition that matter is
composed of atoms or electrons or whatever units physics may at
the moment prefer. As against this latter supposition, I contend
that the ultimate constituents of matter are not atoms or
electrons, but sensations, and other things similar to sensations
as regards extent and duration. As against the view that
introspection reveals a mental world radically different from
sensations, I propose to argue that thoughts, beliefs, desires,
pleasures, pains and emotions are all built up out of sensations
and images alone, and that there is reason to think that images
do not differ from sensations in their intrinsic character. We
thus effect a mutual rapprochement of mind and matter, and reduce
the ultimate data of introspection (in our second sense) to
images alone. On this third view of the meaning of introspection,
therefore, our decision is wholly against it.

There remain two points to be considered concerning
introspection. The first is as to how far it is trustworthy; the
second is as to whether, even granting that it reveals no
radically different STUFF from that revealed by what might be
called external perception, it may not reveal different
RELATIONS, and thus acquire almost as much importance as is
traditionally assigned to it.

To begin with the trustworthiness of introspection. It is common
among certain schools to regard the knowledge of our own mental
processes as incomparably more certain than our knowledge of the
"external" world; this view is to be found in the British
philosophy which descends from Hume, and is present, somewhat
veiled, in Kant and his followers. There seems no reason whatever
to accept this view. Our spontaneous, unsophisticated beliefs,
whether as to ourselves or as to the outer world, are always
extremely rash and very liable to error. The acquisition of
caution is equally necessary and equally difficult in both
directions. Not only are we often un aware of entertaining a
belief or desire which exists in us; we are often actually
mistaken. The fallibility of introspection as regards what we
desire is made evident by psycho-analysis; its fallibility as to
what we know is easily demonstrated. An autobiography, when
confronted by a careful editor with documentary evidence, is
usually found to be full of obviously inadvertent errors. Any of
us confronted by a forgotten letter written some years ago will
be astonished to find how much more foolish our opinions were
than we had remembered them as being. And as to the analysis of
our mental operations--believing, desiring, willing, or what
not--introspection unaided gives very little help: it is
necessary to construct hypotheses and test them by their
consequences, just as we do in physical science. Introspection,
therefore, though it is one among our sources of knowledge, is
not, in isolation, in any degree more trustworthy than "external"

I come now to our second question: Does introspection give us
materials for the knowledge of relations other than those arrived
at by reflecting upon external perception? It might be contended
that the essence of what is "mental" consists of relations, such
as knowing for example, and that our knowledge concerning these
essentially mental relations is entirely derived from
introspection. If "knowing" were an unanalysable relation, this
view would be incontrovertible, since clearly no such relation
forms part of the subject matter of physics. But it would seem
that "knowing" is really various relations, all of them complex.
Therefore, until they have been analysed, our present question
must remain unanswered I shall return to it at the end of the
present course of lectures.


In Lecture V we found reason to think that the ultimate
constituents* of the world do not have the characteristics of
either mind or matter as ordinarily understood: they are not
solid persistent objects moving through space, nor are they
fragments of "consciousness." But we found two ways of grouping
particulars, one into "things" or "pieces of matter," the other
into series of "perspectives," each series being what may be
called a "biography." Before we can define either sensations or
images, it is necessary to consider this twofold classification
in somewhat greater detail, and to derive from it a definition of
perception. It should be said that, in so far as the
classification assumes the whole world of physics (including its
unperceived portions), it contains hypothetical elements. But we
will not linger on the grounds for admitting these, which belong
to the philosophy of physics rather than of psychology.

* When I speak of "ultimate constituents," I do not mean
necessarily such as are theoretically incapable of analysis, but
only such as, at present, we can see no means of analysing. I
speak of such constituents as "particulars," or as "RELATIVE
particulars" when I wish to emphasize the fact that they may be
themselves complex.

The physical classification of particulars collects together all
those that are aspects of one "thing." Given any one particular,
it is found often (we do not say always) that there are a number
of other particulars differing from this one in gradually
increasing degrees. Those (or some of those) that differ from it
only very slightly will be found to differ approximately
according to certain laws which may be called, in a generalized
sense, the laws of "perspective"; they include the ordinary laws
of perspective as a special case. This approximation grows more
and more nearly exact as the difference grows less; in technical
language, the laws of perspective account for the differences to
the first order of small quantities, and other laws are only
required to account for second-order differences. That is to say,
as the difference diminishes, the part of the difference which is
not according to the laws of perspective diminishes much more
rapidly, and bears to the total difference a ratio which tends
towards zero as both are made smaller and smaller. By this means
we can theoretically collect together a number of particulars
which may be defined as the "aspects" or "appearances" of one
thing at one time. If the laws of perspective were sufficiently
known, the connection between different aspects would be
expressed in differential equations.

This gives us, so far, only those particulars which constitute
one thing at one time. This set of particulars may be called a
"momentary thing." To define that series of "momentary things"
that constitute the successive states of one thing is a problem
involving the laws of dynamics. These give the laws governing the
changes of aspects from one time to a slightly later time, with
the same sort of differential approximation to exactness as we
obtained for spatially neighbouring aspects through the laws of
perspective. Thus a momentary thing is a set of particulars,
while a thing (which may be identified with the whole history of
the thing) is a series of such sets of particulars. The
particulars in one set are collected together by the laws of
perspective; the successive sets are collected together by the
laws of dynamics. This is the view of the world which is
appropriate to traditional physics.

The definition of a "momentary thing" involves problems
concerning time, since the particulars constituting a momentary
thing will not be all simultaneous, but will travel outward from
the thing with the velocity of light (in case the thing is in
vacuo). There are complications connected with relativity, but
for our present purpose they are not vital, and I shall ignore

Instead of first collecting together all the particulars
constituting a momentary thing, and then forming the series of
successive sets, we might have first collected together a series
of successive aspects related by the laws of dynamics, and then
have formed the set of such series related by the laws of
perspective. To illustrate by the case of an actor on the stage:
our first plan was to collect together all the aspects which he
presents to different spectators at one time, and then to form
the series of such sets. Our second plan is first to collect
together all the aspects which he presents successively to a
given spectator, and then to do the same thing for the other
spectators, thus forming a set of series instead of a series of
sets. The first plan tells us what he does; the second the
impressions he produces. This second way of classifying
particulars is one which obviously has more relevance to
psychology than the other. It is partly by this second method of
classification that we obtain definitions of one "experience" or
"biography" or "person." This method of classification is also
essential to the definition of sensations and images, as I shall
endeavour to prove later on. But we must first amplify the
definition of perspectives and biographies.

In our illustration of the actor, we spoke, for the moment, as
though each spectator's mind were wholly occupied by the one
actor. If this were the case, it might be possible to define the
biography of one spectator as a series of successive aspects of
the actor related according to the laws of dynamics. But in fact
this is not the case. We are at all times during our waking life
receiving a variety of impressions, which are aspects of a
variety of things. We have to consider what binds together two
simultaneous sensations in one person, or, more generally, any
two occurrences which forte part of one experience. We might say,
adhering to the standpoint of physics, that two aspects of
different things belong to the same perspective when they are in
the same place. But this would not really help us, since a
"place" has not yet been defined. Can we define what is meant by
saying that two aspects are "in the same place," without
introducing anything beyond the laws of perspective and dynamics?

I do not feel sure whether it is possible to frame such a
definition or not; accordingly I shall not assume that it is
possible, but shall seek other characteristics by which a
perspective or biography may be defined.

When (for example) we see one man and hear another speaking at
the same time, what we see and what we hear have a relation which
we can perceive, which makes the two together form, in some
sense, one experience. It is when this relation exists that two
occurrences become associated. Semon's "engram" is formed by all
that we experience at one time. He speaks of two parts of this
total as having the relation of "Nebeneinander" (M. 118; M.E. 33
ff.), which is reminiscent of Herbart's "Zusammen." I think the
relation may be called simply "simultaneity." It might be said
that at any moment all sorts of things that are not part of my
experience are happening in the world, and that therefore the
relation we are seeking to define cannot be merely simultaneity.
This, however, would be an error--the sort of error that the
theory of relativity avoids. There is not one universal time,
except by an elaborate construction; there are only local times,
each of which may be taken to be the time within one biography.
Accordingly, if I am (say) hearing a sound, the only occurrences
that are, in any simple sense, simultaneous with my sensation are
events in my private world, i.e. in my biography. We may
therefore define the "perspective" to which the sensation in
question belongs as the set of particulars that are simultaneous
with this sensation. And similarly we may define the "biography"
to which the sensation belongs as the set of particulars that are
earlier or later than, or simultaneous with, the given sensation.
Moreover, the very same definitions can be applied to particulars
which are not sensations. They are actually required for the
theory of relativity, if we are to give a philosophical
explanation of what is meant by "local time" in that theory The
relations of simultaneity and succession are known to us in our
own experience; they may be analysable, but that does not affect
their suitability for defining perspectives and biographies. Such
time-relations as can be constructed between events in different
biographies are of a different kind: they are not experienced,
and are merely logical, being designed to afford convenient ways
of stating the correlations between different biographies.

It is not only by time-relations that the parts of one biography
are collected together in the case of living beings. In this case
there are the mnemic phenomena which constitute the unity of one
"experience," and transform mere occurrences into "experiences."
I have already dwelt upon the importance of mnemic phenomena for
psychology, and shall not enlarge upon them now, beyond observing
that they are what transforms a biography (in our technical
sense) into a life. It is they that give the continuity of a
"person" or a "mind." But there is no reason to suppose that
mnemic phenomena are associated with biographies except in the
case of animals and plants.

Our two-fold classification of particulars gives rise to the
dualism of body and biography in regard to everything in the
universe, and not only in regard to living things. This arises as
follows. Every particular of the sort considered by physics is a
member of two groups (1) The group of particulars constituting
the other aspects of the same physical object; (2) The group of
particulars that have direct time-relations to the given

Each of these is associated with a place. When I look at a star,
my sensation is (1) A member of the group of particulars which is
the star, and which is associated with the place where the star
is; (2) A member of the group of particulars which is my
biography, and which is associated with the place where I am.*

*I have explained elsewhere the manner in which space is
constructed on this theory, and in which the position of a
perspective is brought into relation with the position of a
physical object ("Our Knowledge of the External World," Lecture
III, pp. 90, 91).

The result is that every particular of the kind relevant to
physics is associated with TWO places; e.g. my sensation of the
star is associated with the place where I am and with the place
where the star is. This dualism has nothing to do with any "mind"
that I may be supposed to possess; it exists in exactly the same
sense if I am replaced by a photographic plate. We may call the
two places the active and passive places respectively.* Thus in
the case of a perception or photograph of a star, the active
place is the place where the star is, while the passive place is
the place where the percipient or photographic plate is.

* I use these as mere names; I do not want to introduce any
notion of "activity."

We can thus, without departing from physics, collect together all
the particulars actively at a given place, or all the particulars
passively at a given place. In our own case, the one group is our
body (or our brain), while the other is our mind, in so far as it
consists of perceptions. In the case of the photographic plate,
the first group is the plate as dealt with by physics, the second
the aspect of the heavens which it photographs. (For the sake of
schematic simplicity, I am ignoring various complications
connected with time, which require some tedious but perfectly
feasible elaborations.) Thus what may be called subjectivity in
the point of view is not a distinctive peculiarity of mind: it is
present just as much in the photographic plate. And the
photographic plate has its biography as well as its "matter." But
this biography is an affair of physics, and has none of the
peculiar characteristics by which "mental" phenomena are
distinguished, with the sole exception of subjectivity.

Adhering, for the moment, to the standpoint of physics, we may
define a "perception" of an object as the appearance of the
object from a place where there is a brain (or, in lower animals,
some suitable nervous structure), with sense-organs and nerves
forming part of the intervening medium. Such appearances of
objects are distinguished from appearances in other places by
certain peculiarities, namely

(1) They give rise to mnemic phenomena;

(2) They are themselves affected by mnemic phenomena.

That is to say, they may be remembered and associated or
influence our habits, or give rise to images, etc., and they are
themselves different from what they would have been if our past
experience had been different--for example, the effect of a
spoken sentence upon the hearer depends upon whether the hearer
knows the language or not, which is a question of past
experience. It is these two characteristics, both connected with
mnemic phenomena, that distinguish perceptions from the
appearances of objects in places where there is no living being.

Theoretically, though often not practically, we can, in our
perception of an object, separate the part which is due to past
experience from the part which proceeds without mnemic influences
out of the character of the object. We may define as "sensation"
that part which proceeds in this way, while the remainder, which
is a mnemic phenomenon, will have to be added to the sensation to
make up what is called the "perception." According to this
definition, the sensation is a theoretical core in the actual
experience; the actual experience is the perception. It is
obvious that there are grave difficulties in carrying out these
definitions, but we will not linger over them. We have to pass,
as soon as we can, from the physical standpoint, which we have
been hitherto adopting, to the standpoint of psychology, in which
we make more use of introspection in the first of the three
senses discussed in the preceding lecture.

But before making the transition, there are two points which must
be made clear. First: Everything outside my own personal
biography is outside my experience; therefore if anything can be
known by me outside my biography, it can only be known in one of
two ways

(1) By inference from things within my biography, or

(2) By some a priori principle independent of experience.

I do not myself believe that anything approaching certainty is to
be attained by either of these methods, and therefore whatever
lies outside my personal biography must be regarded,
theoretically, as hypothesis. The theoretical argument for
adopting the hypothesis is that it simplifies the statement of
the laws according to which events happen in our experience. But
there is no very good ground for supposing that a simple law is
more likely to be true than a complicated law, though there is
good ground for assuming a simple law in scientific practice, as
a working hypothesis, if it explains the facts as well as another
which is less simple. Belief in the existence of things outside
my own biography exists antecedently to evidence, and can only be
destroyed, if at all, by a long course of philosophic doubt. For
purposes of science, it is justified practically by the
simplification which it introduces into the laws of physics. But
from the standpoint of theoretical logic it must be regarded as a
prejudice, not as a well-grounded theory. With this proviso, I
propose to continue yielding to the prejudice.

The second point concerns the relating of our point of view to
that which regards sensations as caused by stimuli external to
the nervous system (or at least to the brain), and distinguishes
images as "centrally excited," i.e. due to causes in the brain
which cannot be traced back to anything affecting the
sense-organs. It is clear that, if our analysis of physical
objects has been valid, this way of defining sensations needs
reinterpretation. It is also clear that we must be able to find
such a new interpretation if our theory is to be admissible.

To make the matter clear, we will take the simplest possible
illustration. Consider a certain star, and suppose for the moment
that its size is negligible. That is to say, we will regard it
as, for practical purposes, a luminous point. Let us further
suppose that it exists only for a very brief time, say a second.
Then, according to physics, what happens is that a spherical wave
of light travels outward from the star through space, just as,
when you drop a stone into a stagnant pond, ripples travel
outward from the place where the stone hit the water. The wave of
light travels with a certain very nearly constant velocity,
roughly 300,000 kilometres per second. This velocity may be
ascertained by sending a flash of light to a mirror, and
observing how long it takes before the reflected flash reaches
you, just as the velocity of sound may be ascertained by means of
an echo.

What it is that happens when a wave of light reaches a given
place we cannot tell, except in the sole case when the place in
question is a brain connected with an eye which is turned in the
right direction. In this one very special case we know what
happens: we have the sensation called "seeing the star." In all
other cases, though we know (more or less hypothetically) some of
the correlations and abstract properties of the appearance of the
star, we do not know the appearance itself. Now you may, for the
sake of illustration, compare the different appearances of the
star to the conjugation of a Greek verb, except that the number
of its parts is really infinite, and not only apparently so to
the despairing schoolboy. In vacuo, the parts are regular, and
can be derived from the (imaginary) root according to the laws of
grammar, i.e. of perspective. The star being situated in empty
space, it may be defined, for purposes of physics, as consisting
of all those appearances which it presents in vacuo, together
with those which, according to the laws of perspective, it would
present elsewhere if its appearances elsewhere were regular. This
is merely the adaptation of the definition of matter which I gave
in an earlier lecture. The appearance of a star at a certain
place, if it is regular, does not require any cause or
explanation beyond the existence of the star. Every regular
appearance is an actual member of the system which is the star,
and its causation is entirely internal to that system. We may
express this by saying that a regular appearance is due to the
star alone, and is actually part of the star, in the sense in
which a man is part of the human race.

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