At the end of our journey it is time to return to the question from
which we set out, namely: What is it that characterizes mind as opposed
to matter? Or, to state the same question in other terms: How is
psychology to be distinguished from physics? The answer provisionally
suggested at the outset of our inquiry was that psychology and physics
are distinguished by the nature of their causal laws, not by their
subject matter. At the same time we held that there is a certain subject
matter, namely images, to which only psychological causal laws are
applicable; this subject matter, therefore, we assigned exclusively to
psychology. But we found no way of defining images except through
their causation; in their intrinsic character they appeared to have no
universal mark by which they could be distinguished from sensations.
In this last lecture I propose to pass in review various suggested
methods of distinguishing mind from matter. I shall then briefly sketch
the nature of that fundamental science which I believe to be the true
metaphysic, in which mind and matter alike are seen to be constructed
out of a neutral stuff, whose causal laws have no such duality as that
of psychology, but form the basis upon which both physics and psychology
are built.
In search for the definition of "mental phenomena," let us begin with
"consciousness," which is often thought to be the essence of mind.
In the first lecture I gave various arguments against the view that
consciousness is fundamental, but I did not attempt to say what
consciousness is. We must find a definition of it, if we are to feel
secure in deciding that it is not fundamental. It is for the sake of the
proof that it is not fundamental that we must now endeavour to decide
what it is.
"Consciousness," by those who regard it as fundamental, is taken to be a
character diffused throughout our mental life, distinct from sensations
and images, memories, beliefs and desires, but present in all of
them.* Dr. Henry Head, in an article which I quoted in Lecture III,
distinguishing sensations from purely physiological occurrences, says:
"Sensation, in the strict sense of the term, demands the existence of
consciousness." This statement, at first sight, is one to which we feel
inclined to assent, but I believe we are mistaken if we do so. Sensation
is the sort of thing of which we MAY be conscious, but not a thing
of which we MUST be conscious. We have been led, in the course of our
inquiry, to admit unconscious beliefs and unconscious desires. There is,
so far as I can see, no class of mental or other occurrences of which we
are always conscious whenever they happen.
* Cf. Lecture VI.
The first thing to notice is that consciousness must be of something. In
view of this, I should define "consciousness" in terms of that relation
of an image of a word to an object which we defined, in Lecture XI, as
"meaning." When a sensation is followed by an image which is a "copy" of
it, I think it may be said that the existence of the image constitutes
consciousness of the sensation, provided it is accompanied by that sort
of belief which, when we reflect upon it, makes us feel that the image
is a "sign" of something other than itself. This is the sort of belief
which, in the case of memory, we expressed in the words "this occurred";
or which, in the case of a judgment of perception, makes us believe
in qualities correlated with present sensations, as e.g., tactile and
visual qualities are correlated. The addition of some element of belief
seems required, since mere imagination does not involve consciousness of
anything, and there can be no consciousness which is not of something.
If images alone constituted consciousness of their prototypes,
such imagination-images as in fact have prototypes would involve
consciousness of them; since this is not the case, an element of belief
must be added to the images in defining consciousness. The belief must
be of that sort that constitutes objective reference, past or
present. An image, together with a belief of this sort concerning it,
constitutes, according to our definition, consciousness of the prototype
of the image.
But when we pass from consciousness of sensations to consciousness of
objects of perception, certain further points arise which demand an
addition to our definition. A judgment of perception, we may say,
consists of a core of sensation, together with associated images, with
belief in the present existence of an object to which sensation and
images are referred in a way which is difficult to analyse. Perhaps we
might say that the belief is not fundamentally in any PRESENT existence,
but is of the nature of an expectation: for example, when we see an
object, we expect certain sensations to result if we proceed to touch
it. Perception, then, will consist of a present sensation together with
expectations of future sensations. (This, of course, is a reflective
analysis, not an account of the way perception appears to unchecked
introspection.) But all such expectations are liable to be erroneous,
since they are based upon correlations which are usual but not
invariable. Any such correlation may mislead us in a particular case,
for example, if we try to touch a reflection in a looking-glass under
the impression that it is "real." Since memory is fallible, a similar
difficulty arises as regards consciousness of past objects. It would
seem odd to say that we can be "conscious" of a thing which does not or
did not exist. The only way to avoid this awkwardness is to add to our
definition the proviso that the beliefs involved in consciousness must
be TRUE.
In the second place, the question arises as to whether we can be
conscious of images. If we apply our definition to this case, it seems
to demand images of images. In order, for example, to be conscious of
an image of a cat, we shall require, according to the letter of the
definition, an image which is a copy of our image of the cat, and has
this image for its prototype. Now, it hardly seems probable, as a matter
of observation, that there are images of images, as opposed to images
of sensations. We may meet this difficulty in two ways, either by boldly
denying consciousness of images, or by finding a sense in which, by
means of a different accompanying belief, an image, instead of meaning
its prototype, can mean another image of the same prototype.
The first alternative, which denies consciousness of images, has already
been discussed when we were dealing with Introspection in Lecture VI. We
then decided that there must be, in some sense, consciousness of images.
We are therefore left with the second suggested way of dealing with
knowledge of images. According to this second hypothesis, there may be
two images of the same prototype, such that one of them means the other,
instead of meaning the prototype. It will be remembered that we defined
meaning by association a word or image means an object, we said, when it
has the same associations as the object. But this definition must not be
interpreted too absolutely: a word or image will not have ALL the
same associations as the object which it means. The word "cat" may
be associated with the word "mat," but it would not happen except by
accident that a cat would be associated with a mat. And in like manner
an image may have certain associations which its prototype will not
have, e.g. an association with the word "image." When these associations
are active, an image means an image, instead of meaning its prototype.
If I have had images of a given prototype many times, I can mean one of
these, as opposed to the rest, by recollecting the time and place or any
other distinctive association of that one occasion. This happens, for
example, when a place recalls to us some thought we previously had in
that place, so that we remember a thought as opposed to the occurrence
to which it referred. Thus we may say that we think of an image A when
we have a similar image B associated with recollections of circumstances
connected with A, but not with its prototype or with other images of the
same prototype. In this way we become aware of images without the
need of any new store of mental contents, merely by the help of new
associations. This theory, so far as I can see, solves the problems of
introspective knowledge, without requiring heroic measures such as those
proposed by Knight Dunlap, whose views we discussed in Lecture VI.
According to what we have been saying, sensation itself is not an
instance of consciousness, though the immediate memory by which it is
apt to be succeeded is so. A sensation which is remembered becomes an
object of consciousness as soon as it begins to be remembered, which
will normally be almost immediately after its occurrence (if at all);
but while it exists it is not an object of consciousness. If, however,
it is part of a perception, say of some familiar person, we may say that
the person perceived is an object of consciousness. For in this case
the sensation is a SIGN of the perceived object in much the same way
in which a memory-image is a sign of a remembered object. The essential
practical function of "consciousness" and "thought" is that they enable
us to act with reference to what is distant in time or space, even
though it is not at present stimulating our senses. This reference
to absent objects is possible through association and habit. Actual
sensations, in themselves, are not cases of consciousness, because they
do not bring in this reference to what is absent. But their connection
with consciousness is very close, both through immediate memory, and
through the correlations which turn sensations into perceptions.
Enough has, I hope, been said to show that consciousness is far too
complex and accidental to be taken as the fundamental characteristic
of mind. We have seen that belief and images both enter into it. Belief
itself, as we saw in an earlier lecture, is complex. Therefore, if any
definition of mind is suggested by our analysis of consciousness, images
are what would naturally suggest themselves. But since we found
that images can only be defined causally, we cannot deal with this
suggestion, except in connection with the difference between physical
and psychological causal laws.
I come next to those characteristics of mental phenomena which arise out
of mnemic causation. The possibility of action with reference to what
is not sensibly present is one of the things that might be held to
characterize mind. Let us take first a very elementary example. Suppose
you are in a familiar room at night, and suddenly the light goes out.
You will be able to find your way to the door without much difficulty
by means of the picture of the room which you have in your mind. In this
case visual images serve, somewhat imperfectly it is true, the purpose
which visual sensations would otherwise serve. The stimulus to the
production of visual images is the desire to get out of the room, which,
according to what we found in Lecture III, consists essentially of
present sensations and motor impulses caused by them. Again, words heard
or read enable you to act with reference to the matters about which they
give information; here, again, a present sensible stimulus, in virtue of
habits formed in the past, enables you to act in a manner appropriate
to an object which is not sensibly present. The whole essence of the
practical efficiency of "thought" consists in sensitiveness to signs:
the sensible presence of A, which is a sign of the present or future
existence of B, enables us to act in a manner appropriate to B. Of
this, words are the supreme example, since their effects as signs are
prodigious, while their intrinsic interest as sensible occurrences on
their own account is usually very slight. The operation of signs may or
may not be accompanied by consciousness. If a sensible stimulus A calls
up an image of B, and we then act with reference to B, we have what may
be called consciousness of B. But habit may enable us to act in a manner
appropriate to B as soon as A appears, without ever having an image of
B. In that case, although A operates as a sign, it operates without the
help of consciousness. Broadly speaking, a very familiar sign tends to
operate directly in this manner, and the intervention of consciousness
marks an imperfectly established habit.
The power of acquiring experience, which characterizes men and animals,
is an example of the general law that, in mnemic causation, the causal
unit is not one event at one time, but two or more events at two or more
times.& A burnt child fears the fire, that is to say, the neighbourhood
of fire has a different effect upon a child which has had the sensations
of burning than upon one which has not. More correctly, the observed
effect, when a child which has been burnt is put near a fire, has for
its cause, not merely the neighbourhood of the fire, but this together
with the previous burning. The general formula, when an animal has
acquired experience through some event A, is that, when B occurs at some
future time, the animal to which A has happened acts differently from
an animal which A has not happened. Thus A and B together, not either
separately, must be regarded as the cause of the animal's behaviour,
unless we take account of the effect which A has had in altering the
animal's nervous tissue, which is a matter not patent to external
observation except under very special circumstances. With this
possibility, we are brought back to causal laws, and to the suggestion
that many things which seem essentially mental are really neural.
Perhaps it is the nerves that acquire experience rather than the mind.
If so, the possibility of acquiring experience cannot be used to define
mind.*
* Cf. Lecture IV.
Very similar considerations apply to memory, if taken as the essence of
mind. A recollection is aroused by something which is happening now,
but is different from the effect which the present occurrence would
have produced if the recollected event had not occurred. This may be
accounted for by the physical effect of the past event on the brain,
making it a different instrument from that which would have resulted
from a different experience. The causal peculiarities of memory may,
therefore, have a physiological explanation. With every special class of
mental phenomena this possibility meets us afresh. If psychology is
to be a separate science at all, we must seek a wider ground for its
separateness than any that we have been considering hitherto.
We have found that "consciousness" is too narrow to characterize mental
phenomena, and that mnemic causation is too wide. I come now to a
characteristic which, though difficult to define, comes much nearer to
what we require, namely subjectivity.
Subjectivity, as a characteristic of mental phenomena, was considered in
Lecture VII, in connection with the definition of perception. We there
decided that those particulars which constitute the physical world can
be collected into sets in two ways, one of which makes a bundle of all
those particulars that are appearances of a given thing from different
places, while the other makes a bundle of all those particulars which
are appearances of different things from a given place. A bundle of
this latter sort, at a given time, is called a "perspective"; taken
throughout a period of time, it is called a "biography." Subjectivity is
the characteristic of perspectives and biographies, the characteristic
of giving the view of the world from a certain place. We saw in Lecture
VII that this characteristic involves none of the other characteristics
that are commonly associated with mental phenomena, such as
consciousness, experience and memory. We found in fact that it is
exhibited by a photographic plate, and, strictly speaking, by any
particular taken in conjunction with those which have the same "passive"
place in the sense defined in Lecture VII. The particulars forming one
perspective are connected together primarily by simultaneity;
those forming one biography, primarily by the existence of direct
time-relations between them. To these are to be added relations
derivable from the laws of perspective. In all this we are clearly not
in the region of psychology, as commonly understood; yet we are also
hardly in the region of physics. And the definition of perspectives
and biographies, though it does not yet yield anything that would
be commonly called "mental," is presupposed in mental phenomena, for
example in mnemic causation: the causal unit in mnemic causation, which
gives rise to Semon's engram, is the whole of one perspective--not of
any perspective, but of a perspective in a place where there is nervous
tissue, or at any rate living tissue of some sort. Perception also,
as we saw, can only be defined in terms of perspectives. Thus the
conception of subjectivity, i.e. of the "passive" place of a particular,
though not alone sufficient to define mind, is clearly an essential
element in the definition.
I have maintained throughout these lectures that the data of psychology
do not differ in, their intrinsic character from the data of physics.
I have maintained that sensations are data for psychology and
physics equally, while images, which may be in some sense exclusively
psychological data, can only be distinguished from sensations by their
correlations, not by what they are in themselves. It is now necessary,
however, to examine the notion of a "datum," and to obtain, if possible,
a definition of this notion.
The notion of "data" is familiar throughout science, and is usually
treated by men of science as though it were perfectly clear.
Psychologists, on the other hand, find great difficulty in the
conception. "Data" are naturally defined in terms of theory of
knowledge: they are those propositions of which the truth is known
without demonstration, so that they may be used as premisses in proving
other propositions. Further, when a proposition which is a datum asserts
the existence of something, we say that the something is a datum, as
well as the proposition asserting its existence. Thus those objects
of whose existence we become certain through perception are said to be
data.
There is some difficulty in connecting this epistemological definition
of "data" with our psychological analysis of knowledge; but until such
a connection has been effected, we have no right to use the conception
"data."
It is clear, in the first place, that there can be no datum apart from a
belief. A sensation which merely comes and goes is not a datum; it only
becomes a datum when it is remembered. Similarly, in perception, we do
not have a datum unless we have a JUDGMENT of perception. In the sense
in which objects (as opposed to propositions) are data, it would seem
natural to say that those objects of which we are conscious are data.
But consciousness, as we have seen, is a complex notion, involving
beliefs, as well as mnemic phenomena such as are required for perception
and memory. It follows that no datum is theoretically indubitable, since
no belief is infallible; it follows also that every datum has a greater
or less degree of vagueness, since there is always some vagueness in
memory and the meaning of images.
Data are not those things of which our consciousness is earliest in
time. At every period of life, after we have become capable of thought,
some of our beliefs are obtained by inference, while others are not.
A belief may pass from either of these classes into the other, and may
therefore become, or cease to be, a belief giving a datum. When, in what
follows, I speak of data, I do not mean the things of which we feel sure
before scientific study begins, but the things which, when a science
is well advanced, appear as affording grounds for other parts of
the science, without themselves being believed on any ground except
observation. I assume, that is to say, a trained observer, with an
analytic attention, knowing the sort of thing to look for, and the sort
of thing that will be important. What he observes is, at the stage of
science which he has reached, a datum for his science. It is just as
sophisticated and elaborate as the theories which he bases upon it,
since only trained habits and much practice enable a man to make
the kind of observation that will be scientifically illuminating.
Nevertheless, when once it has been observed, belief in it is not based
on inference and reasoning, but merely upon its having been seen. In
this way its logical status differs from that of the theories which are
proved by its means.
In any science other than psychology the datum is primarily a
perception, in which only the sensational core is ultimately and
theoretically a datum, though some such accretions as turn the sensation
into a perception are practically unavoidable. But if we postulate an
ideal observer, he will be able to isolate the sensation, and treat this
alone as datum. There is, therefore, an important sense in which we
may say that, if we analyse as much as we ought, our data, outside
psychology, consist of sensations, which include within themselves
certain spatial and temporal relations.
Applying this remark to physiology, we see that the nerves and brain
as physical objects are not truly data; they are to be replaced, in
the ideal structure of science, by the sensations through which the
physiologist is said to perceive them. The passage from these sensations
to nerves and brain as physical objects belongs really to the initial
stage in the theory of physics, and ought to be placed in the reasoned
part, not in the part supposed to be observed. To say we see the
nerves is like saying we hear the nightingale; both are convenient but
inaccurate expressions. We hear a sound which we believe to be causally
connected with the nightingale, and we see a sight which we believe
to be causally connected with a nerve. But in each case it is only
the sensation that ought, in strictness, to be called a datum. Now,
sensations are certainly among the data of psychology. Therefore all the
data of the physical sciences are also psychological data. It remains
to inquire whether all the data of psychology are also data of physical
science, and especially of physiology.
If we have been right in our analysis of mind, the ultimate data of
psychology are only sensations and images and their relations. Beliefs,
desires, volitions, and so on, appeared to us to be complex phenomena
consisting of sensations and images variously interrelated. Thus (apart
from certain relations) the occurrences which seem most distinctively
mental, and furthest removed from physics, are, like physical objects,
constructed or inferred, not part of the original stock of data in the
perfected science. From both ends, therefore, the difference between
physical and psychological data is diminished. Is there ultimately
no difference, or do images remain as irreducibly and exclusively
psychological? In view of the causal definition of the difference
between images and sensations, this brings us to a new question, namely:
Are the causal laws of psychology different from those of any other
science, or are they really physiological?
Certain ambiguities must be removed before this question can be
adequately discussed.
First, there is the distinction between rough approximate laws and
such as appear to be precise and general. I shall return to the former
presently; it is the latter that I wish to discuss now.
Matter, as defined at the end of Lecture V, is a logical fiction,
invented because it gives a convenient way of stating causal laws.
Except in cases of perfect regularity in appearances (of which we can
have no experience), the actual appearances of a piece of matter are not
members of that ideal system of regular appearances which is defined
as being the matter in question. But the matter is, after all, inferred
from its appearances, which are used to VERIFY physical laws. Thus, in
so far as physics is an empirical and verifiable science, it must assume
or prove that the inference from appearances to matter is, in general,
legitimate, and it must be able to tell us, more or less, what
appearances to expect. It is through this question of verifiability and
empirical applicability to experience that we are led to a theory of
matter such as I advocate. From the consideration of this question it
results that physics, in so far as it is an empirical science, not a
logical phantasy, is concerned with particulars of just the same sort
as those which psychology considers under the name of sensations. The
causal laws of physics, so interpreted, differ from those of psychology
only by the fact that they connect a particular with other appearances
in the same piece of matter, rather than with other appearances in the
same perspective. That is to say, they group together particulars having
the same "active" place, while psychology groups together those having
the same "passive" place. Some particulars, such as images, have no
"active" place, and therefore belong exclusively to psychology.
We can now understand the distinction between physics and psychology.
The nerves and brain are matter: our visual sensations when we look
at them may be, and I think are, members of the system constituting
irregular appearances of this matter, but are not the whole of the
system. Psychology is concerned, inter alia, with our sensations when we
see a piece of matter, as opposed to the matter which we see. Assuming,
as we must, that our sensations have physical causes, their causal laws
are nevertheless radically different from the laws of physics, since
the consideration of a single sensation requires the breaking up of
the group of which it is a member. When a sensation is used to verify
physics, it is used merely as a sign of a certain material phenomenon,
i.e. of a group of particulars of which it is a member. But when it is
studied by psychology, it is taken away from that group and put
into quite a different context, where it causes images or voluntary
movements. It is primarily this different grouping that is
characteristic of psychology as opposed to all the physical sciences,
including physiology; a secondary difference is that images, which
belong to psychology, are not easily to be included among the aspects
which constitute a physical thing or piece of matter.
There remains, however, an important question, namely: Are mental events
causally dependent upon physical events in a sense in which the converse
dependence does not hold? Before we can discuss the answer to this
question, we must first be clear as to what our question means.
When, given A, it is possible to infer B, but given B, it is not
possible to infer A, we say that B is dependent upon A in a sense in
which A is not dependent upon B. Stated in logical terms, this amounts
to saying that, when we know a many-one relation of A to B, B is
dependent upon A in respect of this relation. If the relation is a
causal law, we say that B is causally dependent upon A. The illustration
that chiefly concerns us is the system of appearances of a physical
object. We can, broadly speaking, infer distant appearances from near
ones, but not vice versa. All men look alike when they are a mile away,
hence when we see a man a mile off we cannot tell what he will look like
when he is only a yard away. But when we see him a yard away, we can
tell what he will look like a mile away. Thus the nearer view gives us
more valuable information, and the distant view is causally dependent
upon it in a sense in which it is not causally dependent upon the
distant view.
It is this greater causal potency of the near appearance that leads
physics to state its causal laws in terms of that system of regular
appearances to which the nearest appearances increasingly approximate,
and that makes it value information derived from the microscope or
telescope. It is clear that our sensations, considered as irregular
appearances of physical objects, share the causal dependence belonging
to comparatively distant appearances; therefore in our sensational life
we are in causal dependence upon physical laws.
This, however, is not the most important or interesting part of our
question. It is the causation of images that is the vital problem. We
have seen that they are subject to mnenic causation, and that mnenic
causation may be reducible to ordinary physical causation in nervous
tissue. This is the question upon which our attitude must turn towards
what may be called materialism. One sense of materialism is the view
that all mental phenomena are causally dependent upon physical phenomena
in the above-defined sense of causal dependence. Whether this is the
case or not, I do not profess to know. The question seems to me the
same as the question whether mnemic causation is ultimate, which we
considered without deciding in Lecture IV. But I think the bulk of the
evidence points to the materialistic answer as the more probable.
In considering the causal laws of psychology, the distinction between
rough generalizations and exact laws is important. There are many rough
generalizations in psychology, not only of the sort by which we
govern our ordinary behaviour to each other, but also of a more nearly
scientific kind. Habit and association belong among such laws. I will
give an illustration of the kind of law that can be obtained. Suppose a
person has frequently experienced A and B in close temporal contiguity,
an association will be established, so that A, or an image of A, tends
to cause an image of B. The question arises: will the association work
in either direction, or only from the one which has occurred earlier
to the one which has occurred later? In an article by Mr. Wohlgemuth,
called "The Direction of Associations" ("British Journal of Psychology,"
vol. v, part iv, March, 1913), it is claimed to be proved by experiment
that, in so far as motor memory (i.e. memory of movements) is concerned,
association works only from earlier to later, while in visual and
auditory memory this is not the case, but the later of two neighbouring
experiences may recall the earlier as well as the earlier the later.
It is suggested that motor memory is physiological, while visual and
auditory memory are more truly psychological. But that is not the point
which concerns us in the illustration. The point which concerns us
is that a law of association, established by purely psychological
observation, is a purely psychological law, and may serve as a sample
of what is possible in the way of discovering such laws. It is, however,
still no more than a rough generalization, a statistical average. It
cannot tell us what will result from a given cause on a given occasion.
It is a law of tendency, not a precise and invariable law such as those
of physics aim at being.
If we wish to pass from the law of habit, stated as a tendency or
average, to something more precise and invariable, we seem driven to the
nervous system. We can more or less guess how an occurrence produces a
change in the brain, and how its repetition gradually produces something
analogous to the channel of a river, along which currents flow more
easily than in neighbouring paths. We can perceive that in this way, if
we had more knowledge, the tendency to habit through repetition might
be replaced by a precise account of the effect of each occurrence
in bringing about a modification of the sort from which habit would
ultimately result. It is such considerations that make students of
psychophysiology materialistic in their methods, whatever they may be in
their metaphysics. There are, of course, exceptions, such as Professor
J. S. Haldane,* who maintains that it is theoretically impossible to
obtain physiological explanations of psychical phenomena, or physical
explanations of physiological phenomena. But I think the bulk of expert
opinion, in practice, is on the other side.
*See his book, "The New Physiology and Other Addresses"
(Charles Griffin & Co., 1919).
The question whether it is possible to obtain precise causal laws in
which the causes are psychological, not material, is one of detailed
investigation. I have done what I could to make clear the nature of the
question, but I do not believe that it is possible as yet to answer it
with any confidence. It seems to be by no means an insoluble question,
and we may hope that science will be able to produce sufficient grounds
for regarding one answer as much more probable than the other. But for
the moment I do not see how we can come to a decision.
I think, however, on grounds of the theory of matter explained in
Lectures V and VII, that an ultimate scientific account of what goes on
in the world, if it were ascertainable, would resemble psychology rather
than physics in what we found to be the decisive difference between
them. I think, that is to say, that such an account would not be content
to speak, even formally, as though matter, which is a logical fiction,
were the ultimate reality. I think that, if our scientific knowledge
were adequate to the task, which it neither is nor is likely to become,
it would exhibit the laws of correlation of the particulars constituting
a momentary condition of a material unit, and would state the causal
laws* of the world in terms of these particulars, not in terms of
matter. Causal laws so stated would, I believe, be applicable to
psychology and physics equally; the science in which they were stated
would succeed in achieving what metaphysics has vainly attempted, namely
a unified account of what really happens, wholly true even if not the
whole of truth, and free from all convenient fictions or unwarrantable
assumptions of metaphysical entities. A causal law applicable to
particulars would count as a law of physics if it could be stated in
terms of those fictitious systems of regular appearances which are
matter; if this were not the case, it would count as a law of psychology
if one of the particulars were a sensation or an image, i.e. were
subject to mnemic causation. I believe that the realization of the
complexity of a material unit, and its analysis into constituents
analogous to sensations, is of the utmost importance to philosophy, and
vital for any understanding of the relations between mind and matter,
between our perceptions and the world which they perceive. It is in this
direction, I am convinced, that we must look for the solution of many
ancient perplexities.
* In a perfected science, causal laws will take the form of
differential equations--or of finite-difference equations,
if the theory of quanta should prove correct.
It is probable that the whole science of mental occurrences, especially
where its initial definitions are concerned, could be simplified by the
development of the fundamental unifying science in which the causal laws
of particulars are sought, rather than the causal laws of those systems
of particulars that constitute the material units of physics. This
fundamental science would cause physics to become derivative, in the
sort of way in which theories of the constitution of the atom make
chemistry derivative from physics; it would also cause psychology to
appear less singular and isolated among sciences. If we are right in
this, it is a wrong philosophy of matter which has caused many of the
difficulties in the philosophy of mind--difficulties which a right
philosophy of matter would cause to disappear.
The conclusions at which we have arrived may be summed up as follows:
I. Physics and psychology are not distinguished by their material. Mind
and matter alike are logical constructions; the particulars out of which
they are constructed, or from which they are inferred, have various
relations, some of which are studied by physics, others by psychology.
Broadly speaking, physics group particulars by their active places,
psychology by their passive places.
II. The two most essential characteristics of the causal laws which
would naturally be called psychological are SUBJECTIVITY and MNEMIC
CAUSATION; these are not unconnected, since the causal unit in mnemic
causation is the group of particulars having a given passive place at
a given time, and it is by this manner of grouping that subjectivity is
defined.
III. Habit, memory and thought are all developments of mnemic causation.
It is probable, though not certain, that mnemic causation is derivative
from ordinary physical causation in nervous (and other) tissue.
IV. Consciousness is a complex and far from universal characteristic of
mental phenomena.
V. Mind is a matter of degree, chiefly exemplified in number and
complexity of habits.
VI. All our data, both in physics and psychology, are subject to
psychological causal laws; but physical causal laws, at least in
traditional physics, can only be stated in terms of matter, which is
both inferred and constructed, never a datum. In this respect psychology
is nearer to what actually exists.