THE CLASSIFICATION AND THE NOMENCLATURE OF MENTAL OPERATIONS.
If, as has been set forth in the preceding chapter, all mental states
are effects of physical causes, it follows that what are called mental
faculties and operations are, properly speaking, cerebral functions,
allotted to definite, though not yet precisely assignable, parts of the
brain.
These functions appear to be reducible to three groups, namely:
Sensation, Correlation, and Ideation.
The organs of the functions of sensation and correlation are those
portions of the cerebral substance, the molecular changes of which give
rise to impressions of sensation and impressions of relation.
The changes in the nervous matter which bring about the effects which we
call its functions, follow upon some kind of stimulus, and rapidly
reaching their maximum, as rapidly die away. The effect of the
irritation of a nerve-fibre on the cerebral substance with which it is
connected may be compared to the pulling of a long bell-wire. The
impulse takes a little time to reach the bell; the bell rings and then
becomes quiescent, until another pull is given. So, in the brain, every
sensation is the ring of a cerebral particle, the effect of a momentary
impulse sent along a nerve-fibre.
If there were a complete likeness between the two terms of this very
rough and ready comparison, it is obvious that there could be no such
thing as memory. A bell records no audible sign of having been rung five
minutes ago, and the activity of a sensigenous cerebral particle might
similarly leave no trace. Under these circumstances, again, it would
seem that the only impressions of relation which could arise would be
those of co-existence and of similarity. For succession implies memory
of an antecedent state.[24]
But the special peculiarity of the cerebral apparatus is, that any given
function which has once been performed is very easily set a-going again,
by causes more or less different from those to which it owed its origin.
Of the mechanism of this generation of images of impressions or ideas
(in Hume's sense), which may be termed _Ideation_, we know nothing at
present, though the fact and its results are familiar enough.
During our waking, and many of our sleeping, hours, in fact, the
function of ideation is in continual, if not continuous, activity.
Trains of thought, as we call them, succeed one another without
intermission, even when the starting of new trains by fresh
sense-impressions is as far as possible prevented. The rapidity and the
intensity of this ideational process are obviously dependent upon
physiological conditions. The widest differences in these respects are
constitutional in men of different temperaments; and are observable in
oneself, under varying conditions of hunger and repletion, fatigue and
freshness, calmness and emotional excitement. The influence of diet on
dreams; of stimulants upon the fulness and the velocity of the stream of
thought; the delirious phantasms generated by disease, by hashish, or by
alcohol; will occur to every one as examples of the marvellous
sensitiveness of the apparatus of ideation to purely physical
influences.
The succession of mental states in ideation is not fortuitous, but
follows the law of association, which may be stated thus: that every
idea tends to be followed by some other idea which is associated with
the first, or its impression, by a relation of succession, of
contiguity, or of likeness.
Thus the idea of the word horse just now presented itself to my mind,
and was followed in quick succession by the ideas of four legs, hoofs,
teeth, rider, saddle, racing, cheating; all of which ideas are connected
in my experience with the impression, or the idea, of a horse and with
one another, by the relations of contiguity and succession. No great
attention to what passes in the mind is needful to prove that our trains
of thought are neither to be arrested, nor even permanently controlled,
by our desires or emotions. Nevertheless they are largely influenced by
them. In the presence of a strong desire, or emotion, the stream of
thought no longer flows on in a straight course, but seems, as it were,
to eddy round the idea of that which is the object of the emotion. Every
one who has "eaten his bread in sorrow" knows how strangely the current
of ideas whirls about the conception of the object of regret or remorse
as a centre; every now and then, indeed, breaking away into the new
tracks suggested by passing associations, but still returning to the
central thought. Few can have been so happy as to have escaped the
social bore, whose pet notion is certain to crop up whatever topic is
started; while the fixed idea of the monomaniac is but the extreme form
of the same phenomenon.
And as, on the one hand, it is so hard to drive away the thought we
would fain be rid of; so, upon the other, the pleasant imaginations
which we would so gladly retain are, sooner or later, jostled away by
the crowd of claimants for birth into the world of consciousness; which
hover as a sort of psychical possibilities, or inverse ghosts, the
bodily presentments of spiritual phenomena to be, in the limbo of the
brain. In that form of desire which is called "attention," the train of
thought, held fast, for a time, in the desired direction, seems ever
striving to get on to another line--and the junctions and sidings are so
multitudinous!
The constituents of trains of ideas may be grouped in various ways.
Hume says:--
"We find, by experience, that when any impression has been present
in the mind, it again makes its appearance there as an idea, and
this it may do in two different ways: either when, on its new
appearance, it retains a considerable degree of its first vivacity,
and is somewhat intermediate between an impression and an idea; or
when it entirely loses that vivacity, and is a perfect idea. The
faculty by which we repeat our impressions in the first manner, is
called the _memory_, and the other the _imagination_."--(I. pp. 23,
24.)
And he considers that the only difference between ideas of imagination
and those of memory, except the superior vivacity of the latter, lies
in the fact that those of memory preserve the original order of the
impressions from which they are derived, while the imagination "is free
to transpose and change its ideas."
The latter statement of the difference between memory and imagination is
less open to cavil than the former, though by no means unassailable.
The special characteristic of a memory surely is not its vividness; but
that it is a complex idea, in which the idea of that which is remembered
is related by co-existence with other ideas, and by antecedence with
present impressions.
If I say I remember A. B., the chance acquaintance of ten years ago, it
is not because my idea of A. B. is very vivid--on the contrary, it is
extremely faint--but because that idea is associated with ideas of
impressions co-existent with those which I call A. B.; and that all
these are at the end of the long series of ideas, which represent that
much past time. In truth I have a much more vivid idea of Mr. Pickwick,
or of Colonel Newcome, than I have of A. B.; but, associated with the
ideas of these persons, I have no idea of their having ever been derived
from the world of impressions; and so they are relegated to the world of
imagination. On the other hand, the characteristic of an imagination may
properly be said to lie not in its intensity, but in the fact that, as
Hume puts it, "the arrangement," or the relations, of the ideas are
different from those in which the impressions, whence these ideas are
derived, occurred; or in other words, that the thing imagined has not
happened. In popular usage, however, imagination is frequently employed
for simple memory--"In imagination I was back in the old times."
It is a curious omission on Hume's part that, while thus dwelling on two
classes of ideas, _Memories_ and _Imaginations_, he has not, at the same
time, taken notice of a third group, of no small importance, which are
as different from imaginations as memories are; though, like the latter,
they are often confounded with pure imaginations in general speech.
These are the ideas of expectation, or as they may be called for the
sake of brevity, _Expectations_; which differ from simple imaginations
in being associated with the idea of the existence of corresponding
impressions, in the future, just as memories contain the idea of the
existence of the corresponding impressions in the past.
The ideas belonging to two of the three groups enumerated: namely,
memories and expectations, present some features, of particular
interest. And first, with respect to memories.
In Hume's words, all simple ideas are copies of simple impressions. The
idea of a single sensation is a faint, but accurate, image of that
sensation; the idea of a relation is a reproduction of the feeling of
co-existence, of succession, or of similarity. But, when complex
impressions or complex ideas are reproduced as memories, it is probable
that the copies never give all the details of the originals with perfect
accuracy, and it is certain that they rarely do so. No one possesses a
memory so good, that if he has only once observed a natural object, a
second inspection does not show him something that he has forgotten.
Almost all, if not all, our memories are therefore sketches, rather than
portraits, of the originals--the salient features are obvious, while the
subordinate characters are obscure or unrepresented.
Now, when several complex impressions which are more or less different
from one another--let us say that out of ten impressions in each, six
are the same in all, and four are different from all the rest--are
successively presented to the mind, it is easy to see what must be the
nature of the result. The repetition of the six similar impressions will
strengthen the six corresponding elements of the complex idea, which
will therefore acquire greater vividness; while the four differing
impressions of each will not only acquire no greater strength than they
had at first, but, in accordance with the law of association, they will
all tend to appear at once, and will thus neutralise one another.
This mental operation may be rendered comprehensible by considering what
takes place in the formation of compound photographs--when the images of
the faces of six sitters, for example, are each received on the same
photographic plate, for a sixth of the time requisite to take one
portrait. The final result is that all those points in which the six
faces agree are brought out strongly, while all those in which they
differ are left vague; and thus what may be termed a _generic_ portrait
of the six, in contradistinction to a _specific_ portrait of any one, is
produced.
Thus our ideas of single complex impressions are incomplete in one way,
and those of numerous, more or less similar, complex impressions are
incomplete in another way; that is to say, they are _generic_, not
_specific_. And hence it follows, that our ideas of the impressions in
question are not, in the strict sense of the word, copies of those
impressions; while, at the same time, they may exist in the mind
independently of language.
The generic ideas which are formed from several similar, but not
identical, complex experiences are what are commonly called _abstract_
or _general_ ideas; and Berkeley endeavoured to prove that all general
ideas are nothing but particular ideas annexed to a certain term, which
gives them a more extensive signification, and makes them recall, upon
occasion, other individuals which are similar to them. Hume says that he
regards this as "one of the greatest and the most valuable discoveries
that has been made of late years in the republic of letters," and
endeavours to confirm it in such a manner that it shall be "put beyond
all doubt and controversy."
I may venture to express a doubt whether he has succeeded in his object;
but the subject is an abstruse one; and I must content myself with the
remark, that though Berkeley's view appears to be largely applicable to
such general ideas as are formed after language has been acquired, and
to all the more abstract sort of conceptions, yet that general ideas of
sensible objects may nevertheless be produced in the way indicated, and
may exist independently of language. In dreams, one sees houses, trees
and other objects, which are perfectly recognisable as such, but which
remind one of the actual objects as seen "out of the corner of the eye,"
or of the pictures thrown by a badly-focussed magic lantern. A man
addresses us who is like a figure seen by twilight; or we travel through
countries where every feature of the scenery is vague; the outlines of
the hills are ill-marked, and the rivers have no defined banks. They
are, in short, generic ideas of many past impressions of men, hills, and
rivers. An anatomist who occupies himself intently with the examination
of several specimens of some new kind of animal, in course of time
acquires so vivid a conception of its form and structure, that the idea
may take visible shape and become a sort of waking dream. But the figure
which thus presents itself is generic, not specific. It is no copy of
any one specimen, but, more or less, a mean of the series; and there
seems no reason to doubt that the minds of children before they learn to
speak, and of deaf mutes, are peopled with similarly generated generic
ideas of sensible objects.
It has been seen that a memory is a complex idea made up of at least two
constituents. In the first place there is the idea of an object; and
secondly, there is the idea of the relation of antecedence between that
object and some present objects.
To say that one has a recollection of a given event and to express the
belief that it happened, are two ways of giving an account of one and
the same mental fact. But the former mode of stating the fact of memory
is preferable, at present, because it certainly does not presuppose the
existence of language in the mind of the rememberer; while it may be
said that the latter does. It is perfectly possible to have the idea of
an event A, and of the events B, C, D, which came between it and the
present state E, as mere mental pictures. It is hardly to be doubted
that children have very distinct memories long before they can speak;
and we believe that such is the case because they act upon their
memories. But, if they act upon their memories, they to all intents and
purposes believe their memories. In other words, though, being devoid of
language, the child cannot frame a proposition expressive of belief;
cannot say "sugar-plum was sweet;" yet the psychical operation of which
that proposition is merely the verbal expression, is perfectly
effected. The experience of the co-existence of sweetness with sugar has
produced a state of mind which bears the same relation to a verbal
proposition, as the natural disposition to produce a given idea, assumed
to exist by Descartes as an "innate idea" would bear to that idea put
into words.
The fact that the beliefs of memory precede the use of language, and
therefore are originally purely instinctive, and independent of any
rational justification, should have been of great importance to Hume,
from its bearing upon his theory of causation; and it is curious that he
has not adverted to it, but always takes the trustworthiness of memories
for granted. It may be worth while briefly to make good the omission.
That I was in pain, yesterday, is as certain to me as any matter of fact
can be; by no effort of the imagination is it possible for me really to
entertain the contrary belief. At the same time, I am bound to admit,
that the whole foundation for my belief is the fact, that the idea of
pain is indissolubly associated in my mind with the idea of that much
past time. Any one who will be at the trouble may provide himself with
hundreds of examples to the same effect.
This and similar observations are important under another aspect. They
prove that the idea of even a single strong impression may be so
powerfully associated with that of a certain time, as to originate a
belief of which the contrary is inconceivable, and which may therefore
be properly said to be necessary. A single weak, or moderately strong,
impression may not be represented by any memory. But this defect of weak
experiences may be compensated by their repetition; and what Hume means
by "custom" or "habit" is simply the repetition of experiences.
"wherever the repetition of any particular act or operation
produces a propensity to renew the same act or operation, without
being impelled by any reasoning or process of the understanding, we
always say that this propensity is the effect of _Custom_. By
employing that word, we pretend not to have given the ultimate
reason of such a propensity. We only point out a principle of human
nature which is universally acknowledged, and which is well known
by its effects."--(IV. p. 52.)
It has been shown that an expectation is a complex idea which, like a
memory, is made up of two constituents. The one is the idea of an
object, the other is the idea of a relation of sequence between that
object and some present object; and the reasoning which applied to
memories applies to expectations. To have an expectation[25] of a given
event, and to believe that it will happen, are only two modes of stating
the same fact. Again, just in the same way as we call a memory, put into
words, a belief, so we give the same name to an expectation in like
clothing. And the fact already cited, that a child before it can speak
acts upon its memories, is good evidence that it forms expectations. The
infant who knows the meaning neither of "sugar-plum" nor of "sweet,"
nevertheless is in full possession of that complex idea, which, when he
has learned to employ language, will take the form of the verbal
proposition, "A sugar-plum will be sweet."
Thus, beliefs of expectation, or at any rate their potentialities, are,
as much as those of memory, antecedent to speech, and are as incapable
of justification by any logical process. In fact, expectations are but
memories inverted. The association which is the foundation of
expectation must exist as a memory before it can play its part. As Hume
says,--
" ... it is certain we here advance a very intelligible proposition
at least, if not a true one, when we assert that after the constant
conjunction of two objects, heat and flame, for instance, weight
and solidity, we are determined by custom alone to expect the one
from the appearance of the other. This hypothesis seems even the
only one which explains the difficulty why we draw from a thousand
instances, an inference which we are not able to draw from one
instance, that is in no respect different from them."...
"Custom, then, is the great guide of human life. It is that
principle alone which renders our experience useful to us, and
makes us expect, for the future, a similar train of events with
those which have appeared in the past."...
"All belief of matter-of-fact or real existence is derived merely
from some object present to the memory or senses, and a customary
conjunction between that and some other object; or in other words,
having found, in many instances, that any two kinds of objects,
flame and heat, snow and cold, have always been conjoined together:
if flame or snow be presented anew to the senses, the mind is
carried by custom to expect heat or cold, and to _believe_ that
such a quality does exist, and will discover itself upon a nearer
approach. This belief is the necessary result of placing the mind
in such circumstances. It is an operation of the soul, when we are
so situated, as unavoidable as to feel the passion of love, when we
receive benefits, or hatred, when we meet with injuries. All these
operations are a species of natural instincts, which no reasoning
or process of the thought and understanding is able either to
produce or to prevent."--(IV. pp. 52-56.)
The only comment that appears needful here is, that Hume has attached
somewhat too exclusive a weight to that repetition of experiences to
which alone the term "custom" can be properly applied. The proverb says
that "a burnt child dreads the fire"; and any one who will make the
experiment will find, that one burning is quite sufficient to establish
an indissoluble belief that contact with fire and pain go together.
As a sort of inverted memory, expectation follows the same laws; hence,
while a belief of expectation is, in most cases, as Hume truly says,
established by custom, or the repetition of weak impressions, it may
quite well be based upon a single strong experience. In the absence of
language, a specific memory cannot be strengthened by repetition. It is
obvious that that which has happened cannot happen again, with the same
collateral associations of co-existence and succession. But, memories of
the co-existence and succession of impressions are capable of being
indefinitely strengthened by the recurrence of similar impressions, in
the same order, even though the collateral associations are totally
different; in fact, the ideas of these impressions become generic.
If I recollect that a piece of ice was cold yesterday, nothing can
strengthen the recollection of that particular fact; on the contrary, it
may grow weaker, in the absence of any record of it. But if I touch ice
to-day and again find it cold, the association is repeated, and the
memory of it becomes stronger. And, by this very simple process of
repetition of experience, it has become utterly impossible for us to
think of having handled ice without thinking of its coldness. But, that
which is, under the one aspect, the strengthening of a memory, is,
under the other, the intensification of an expectation. Not only can we
not think of having touched ice, without feeling cold, but we cannot
think of touching ice, in the future, without expecting to feel cold. An
expectation so strong that it cannot be changed, or abolished, may thus
be generated out of repeated experiences. And it is important to note
that such expectations may be formed quite unconsciously. In my dressing
room, a certain can is usually kept full of water, and I am in the habit
of lifting it to pour out water for washing. Sometimes the servant has
forgotten to fill it, and then I find that, when I take hold of the
handle, the can goes up with a jerk. Long association has, in fact, led
me to expect the can to have a considerable weight; and, quite unawares,
my muscular effort is adjusted to the expectation.
The process of strengthening generic memories of succession, and, at the
same time, intensifying expectations of succession, is what is commonly
called _verification_. The impression B has frequently been observed to
follow the impression A. The association thus produced is represented as
the memory, A -> B. When the impression A appears again, the idea of B
follows, associated with that of the immediate appearance of the
impression B. If the impression B does appear, the expectation is said
to be verified; while the memory A -> B is strengthened, and gives rise
in turn to a stronger expectation. And repeated verification may render
that expectation so strong that its non-verification is inconceivable.
FOOTNOTES:
[24] It is not worth while, for the present purpose, to consider
whether, as all nervous action occupies a sensible time, the duration of
one impression might not overlap that of the impression which follows
it, in the case supposed.
[25] We give no name to faint memories; but expectations of like
character play so large a part in human affairs that they, together with
the associated emotions of pleasure and pain, are distinguished as
"hopes" or "fears."