The Analysis of Mind, Bertrand Russell [best desktop ebook reader .txt] 📗

in SOME sense they

are “unreal.” But this difference is hard to analyse or state

correctly. What we call the “unreality” of images requires

interpretation it cannot mean what would be expressed by saying

“there’s no such thing.” Images are just as truly part of the

actual world as sensations are. All that we really mean by

calling an image “unreal” is that it does not have the

concomitants which it would have if it were a sensation. When we

call up a visual image of a chair, we do not attempt to sit in

it, because we know that, like Macbeth’s dagger, it is not

“sensible to feeling as to sight”— i.e. it does not have the

correlations with tactile sensations which it would have if it

were a visual sensation and not merely a visual image. But this

means that the so-called “unreality” of images consists merely in

their not obeying the laws of physics, and thus brings us back to

the causal distinction between images and sensations.

 

This view is confirmed by the fact that we only feel images to be

“unreal” when we already know them to be images. Images cannot be

defined by the FEELING of unreality, because when we falsely

believe an image to be a sensation, as in the case of dreams, it

FEELS just as real as if it were a sensation. Our feeling of

unreality results from our having already realized that we are

dealing with an image, and cannot therefore be the definition of

what we mean by an image. As soon as an image begins to deceive

us as to its status, it also deceives us as to its correlations,

which are what we mean by its “reality.”

 

(3) This brings us to the third mode of distinguishing images

from sensations, namely, by their causes and effects. I believe

this to be the only valid ground of distinction. James, in the

passage about the mental fire which won’t burn real sticks,

distinguishes images by their effects, but I think the more

reliable distinction is by their causes. Professor Stout (loc.

cit., p. 127) says: “One characteristic mark of what we agree in

calling sensation is its mode of production. It is caused by what

we call a STIMULUS. A stimulus is always some condition external

to the nervous system itself and operating upon it.” I think that

this is the correct view, and that the distinction between images

and sensations can only be made by taking account of their

causation. Sensations come through sense-organs, while images do

not. We cannot have visual sensations in the dark, or with our

eyes shut, but we can very well have visual images under these

circumstances. Accordingly images have been defined as “centrally

excited sensations,” i.e. sensations which have their

physiological cause in the brain only, not also in the

sense-organs and the nerves that run from the sense-organs to the

brain. I think the phrase “centrally excited sensations” assumes

more than is necessary, since it takes it for granted that an

image must have a proximate physiological cause. This is probably

true, but it is an hypothesis, and for our purposes an

unnecessary one. It would seem to fit better with what we can

immediately observe if we were to say that an image is

occasioned, through association, by a sensation or another image,

in other words that it has a mnemic cause—which does not prevent

it from also having a physical cause. And I think it will be

found that the causation of an image always proceeds according to

mnemic laws, i.e. that it is governed by habit and past

experience. If you listen to a man playing the pianola without

looking at him, you will have images of his hands on the keys as

if he were playing the piano; if you suddenly look at him while

you are absorbed in the music, you will experience a shock of

surprise when you notice that his hands are not touching the

notes. Your image of his hands is due to the many times that you

have heard similar sounds and at the same time seen the player’s

hands on the piano. When habit and past experience play this

part, we are in the region of mnemic as opposed to ordinary

physical causation. And I think that, if we could regard as

ultimately valid the difference between physical and mnemic

causation, we could distinguish images from sensations as having

mnemic causes, though they may also have physical causes.

Sensations, on the other hand, will only have physical causes.

 

However this may be, the practically effective distinction

between sensations and images is that in the causation of

sensations, but not of images, the stimulation of nerves carrying

an effect into the brain, usually from the surface of the body,

plays an essential part. And this accounts for the fact that

images and sensations cannot always be distinguished by their

intrinsic nature.

 

Images also differ from sensations as regards their effects.

Sensations, as a rule, have both physical and mental effects. As

you watch the train you meant to catch leaving the station, there

are both the successive positions of the train (physical effects)

and the successive waves of fury and disappointment (mental

effects). Images, on the contrary, though they MAY produce bodily

movements, do so according to mnemic laws, not according to the

laws of physics. All their effects, of whatever nature, follow

mnemic laws. But this difference is less suitable for definition

than the difference as to causes.

 

Professor Watson, as a logical carrying-out of his behaviourist

theory, denies altogether that there are any observable phenomena

such as images are supposed to be. He replaces them all by faint

sensations, and especially by pronunciation of words sotto voce.

When we “think” of a table (say), as opposed to seeing it, what

happens, according to him, is usually that we are making small

movements of the throat and tongue such as would lead to our

uttering the word “table” if they were more pronounced. I shall

consider his view again in connection with words; for the present

I am only concerned to combat his denial of images. This denial

is set forth both in his book on “Behavior” and in an article

called “Image and Affection in Behavior” in the “Journal of

Philosophy, Psychology and Scientific Methods,” vol. x (July,

1913). It seems to me that in this matter he has been betrayed

into denying plain facts in the interests of a theory, namely,

the supposed impossibility of introspection. I dealt with the

theory in Lecture VI; for the present I wish to reinforce the

view that the facts are undeniable.

 

Images are of various sorts, according to the nature of the

sensations which they copy. Images of bodily movements, such as

we have when we imagine moving an arm or, on a smaller scale,

pronouncing a word, might possibly be explained away on Professor

Watson’s lines, as really consisting in small incipient movements

such as, if magnified and prolonged, would be the movements we

are said to be imagining. Whether this is the case or not might

even be decided experimentally. If there were a delicate

instrument for recording small movements in the mouth and throat,

we might place such an instrument in a person’s mouth and then

tell him to recite a poem to himself, as far as possible only in

imagination. I should not be at all surprised if it were found

that actual small movements take place while he is “mentally”

saying over the verses. The point is important, because what is

called “thought” consists mainly (though I think not wholly) of

inner speech. If Professor Watson is right as regards inner

speech, this whole region is transferred from imagination to

sensation. But since the question is capable of experimental

decision, it would be gratuitous rashness to offer an opinion

while that decision is lacking.

 

But visual and auditory images are much more difficult to deal

with in this way, because they lack the connection with physical

events in the outer world which belongs to visual and auditory

sensations. Suppose, for example, that I am sitting in my room,

in which there is an empty arm-chair. I shut my eyes, and call up

a visual image of a friend sitting in the arm-chair. If I thrust

my image into the world of physics, it contradicts all the usual

physical laws. My friend reached the chair without coming in at

the door in the usual way; subsequent inquiry will show that he

was somewhere else at the moment. If regarded as a sensation, my

image has all the marks of the supernatural. My image, therefore,

is regarded as an event in me, not as having that position in the

orderly happenings of the public world that belongs to

sensations. By saying that it is an event in me, we leave it

possible that it may be PHYSIOLOGICALLY caused: its privacy may

be only due to its connection with my body. But in any case it is

not a public event, like an actual person walking in at the door

and sitting down in my chair. And it cannot, like inner speech,

be regarded as a SMALL sensation, since it occupies just as large

an area in my visual field as the actual sensation would do.

 

Professor Watson says: “I should throw out imagery altogether and

attempt to show that all natural thought goes on in terms of

sensori-motor processes in the larynx.” This view seems to me

flatly to contradict experience. If you try to persuade any

uneducated person that she cannot call up a visual picture of a

friend sitting in a chair, but can only use words describing what

such an occurrence would be like, she will conclude that you are

mad. (This statement is based upon experiment.) Galton, as every

one knows, investigated visual imagery, and found that education

tends to kill it: the Fellows of the Royal Society turned out to

have much less of it than their wives. I see no reason to doubt

his conclusion that the habit of abstract pursuits makes learned

men much inferior to the average in power of visualizing, and

much more exclusively occupied with words in their “thinking.”

And Professor Watson is a very learned man.

 

I shall henceforth assume that the existence of images is

admitted, and that they are to be distinguished from sensations

by their causes, as well as, in a lesser degree, by their

effects. In their intrinsic nature, though they often differ from

sensations by being more dim or vague or faint, yet they do not

always or universally differ from sensations in any way that can

be used for defining them. Their privacy need form no bar to the

scientific study of them, any more than the privacy of bodily

sensations does. Bodily sensations are admitted by even the most

severe critics of introspection, although, like images, they can

only be observed by one observer. It must be admitted, however,

that the laws of the appearance and disappearance of images are

little known and difficult to discover, because we are not

assisted, as in the case of sensations, by our knowledge of the

physical world.

 

There remains one very important point concerning images, which

will occupy us much hereafter, and that is, their resemblance to

previous sensations. They are said to be “copies” of sensations,

always as regards the simple qualities that enter into them,

though not always as regards the manner in which these are put

together. It is generally believed that we cannot imagine a shade

of colour that we have never seen, or a sound that we have never

heard. On this subject Hume is the classic. He says, in the

definitions already quoted:

 

“Those perceptions, which enter with most force and violence, we

may name