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 them.
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 particular.
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.
But presently the light of the star reaches our atmosphere. It begins
to be refracted, and dimmed by mist, and its velocity is slightly
diminished. At last it reaches a human eye, where a complicated process
takes place, ending in a sensation which gives us our grounds for
believing in all that has gone before. Now, the irregular appearances of
the star are not, strictly speaking, members of the system which is the
star, according to our definition of matter. The irregular appearances,
however, are not merely irregular: they proceed according to laws which
can be stated in terms of the matter through which the light has
passed on its way. The sources of an irregular appearance are therefore
twofold:
(1) The object which is appearing irregularly;