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difficulty in the way of supposing that perceptions are caused by the brain. Perception is something mental, and the brain is something physical; and, though we have a clear idea of the interaction of physical things, as of the way in which one physical thing causes another to move, we cannot conceive the action of a physical thing on a mental thing, or vice versa.

This brings us to the second kind of difficulty as to the relation between mind and matter—that concerning the union of body and soul. It certainly seems as if there were some kind of very close connexion between many of my mental states and the movements of various parts of my body, so close indeed that changes in my body seem constantly to produce changes in my mind, and vice versa. In fact, few things seem more certain than that a mental event-for instance, the desire to drink-may be one of the causes of a series of physical events—for instance, of my raising a glass of wine and pouring the contents down my throat. Nor does it seem less certain that physical events—for instance, the action of the wine on my nerves and blood-may cause a mental event; the changes in my nerves and blood, for instance, may make me feel more cheerful. It seems certain that events like these happen; and the majority of them do not seem at all mysterious. Philosophers, however, have discovered various difficulties in understanding them. My mind, we have seen, is something with no analogy to my body; for one thing, it is not extended in space, whereas my body is. We have already noticed the puzzle as to how there can be a causal relation between the mental and the physical; when we add that the mind, with all its feelings, volitions, and perceptions, is not in space, does not seem to occupy any area, we seem to have fixed a gulf between body and mind which there is no means of bridging. What, then, can be meant by speaking of their union ?

Some philosophers hold that there are no fatal objections to the common-sense view. Thus Mr McDougall argues in his book, 'Body and Mind,' that mental changes, besides causing one another, also cause bodily changes, and vice versa; and he tries to show that the usual scientific objection, that this hypothesis violates the law of the conservation of energy, is ill-founded. Whether he has succeeded in showing this may be doubted. His position suffers from his coupling with it the view that the soul is an indivisible entity. This may be true; but his arguments on this head are unconvincing, and it does not seem to be the case, as he supposes, that the hypothesis of psycho-physical interaction must stand or fall with that of the unitary Ego. But we must return to Bergson.

We have noticed (though he does not state them very clearly) some of the chief difficulties which he thinks that he has solved in Matière et Mémoire'; and the leading idea in his solution is as follows. Previous philosophers have failed to solve these difficulties because they have all started by assuming, in one way or another, that mind is something different in kind from matter. If mind and matter are different in kind, it must be impossible, however ingeniously we theorise, to understand what perception of a material object by a mind is, or how it arises, or how soul and body can be united; for how can there be any sort of connexion between two utterly disparate things ? But suppose that mind and matter are at bottom very much the same sort of thing --and it is common sense, he says, to suppose this—then all the difficulties vanish. And one of the means by which he tries to make this supposition plausible is by pointing out that all material objects are 'images'; the material universe, he says, is composed entirely of images acting and reacting upon one another. This is, in his opinion, a first step towards understanding the connexion between mind and matter, because to realise that material objects are images is to see that mind, with its faculty of representation, has something in common with matter.

Let us first see how he applies this definition to the difficulties which occur in considering what is meant by saying that we perceive material objects. If material

. objects are images, then, strictly speaking, the word 'perception' will mean, he thinks, the totality of images in the universe. This totality is 'given’; that is to say, all the material objects in the universe co-exist at any one moment. But if perception is thus 'given 'de jure, it is limited de facto. I do not perceive all the material objects in the universe, though all of them are acting on

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that image which is my body. We have thus transposed the traditional difficulties as to perception ; for we now see that what needs explanation is not why we perceive anything, but rather why we do not in practice perceive everything And he explains this by arguing that the function of the body is to limit the life of the mind, and that with a view to action.

This idea that perception has some essential reference to action is one of Bergson's most characteristic doctrines, but owing to the extreme ambiguity of his language it is very difficult to express precisely. What he has chiefly in mind is, perhaps, the contrast between the apparently free action of human beings and the necessary mutual determination of interacting physical particles. When one lifeless material object A acts on another B, B's movement is necessarily determined according to physical or chemical laws; and this, he thinks, is the same thing as to say that B has no choice. But there have arisen in the universe (how, it will be the object of L'Evolution Créatrice’ to explain) material objects which are not lifeless--organised bodies of every degree of complexity from a protoplasmic cell to a man; and the movement of these bodies is determined according to no law and can be expressed by no mathematical formula. For their peculiarity is that they possess an apparatus—in vertebrates, the nervous system and brain-which enables them, on the reception of shocks from surrounding objects, to choose between a number of possible actions ; they are, as he puts it, 'centres of indetermination.'

Thus the function of the brain and nerves is not in any sense to store up or engender representations, but merely to prepare the reaction of the body to the action of external objects. Perception,' he says, which progresses in proportion to the complication of the nervous system, is wholly orientated towards action, and not towards pure knowledge.' We now begin to see what • I see a table' means. It means that, thanks to my nervous system, certain material objects, namely those which at the moment interest my action, prepare in my body movements which will be useful to it. In some sense, perhaps, I might be said to perceive all the other images in the universe as well, since they too are 'given’; but it is only this small residue that I actually perceive,

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the machinery of my nerves entangling, with a view to action, only those images that are important, and letting the rest slip by.

Thus, firstly, not only is the puzzle as to the object of perception solved, but also the puzzle as to what perception is. It is no longer something merely mental, so that we cannot understand how brain-states could produce it or store it up. It is part of matter; it is in, he constantly says, material objects themselves; it is the prolongation, with a view to action, of the complex whole formed by the external object, and the sensorimotor mechanism of my nerves and brain. And, secondly, Bergson thinks that the difficulty as to the union of soul and body is also solved. While it was impossible to understand how a cerebral state could cause a mental state, it is quite easy to see that a cerebral state can cause a perception if a perception is something physical. Soul and body can be united because at bottom they are much the same sort of thing.

Thus what Bergson thinks that he has established by this argument is, first of all, a certain view as to the nature of our minds. Our minds are not, as philosophers have got into inextricable difficulties by supposing, unextended and extra-spatial things; on the contrary, in so far as they are pure perception, they are parts of matter, and, like matter, extended in space. But he also considers himself, by the same process, to have established a certain view as to the nature of matter; just as mind, in so far as pure perception, is extended matter, so matter, in so far as perceived, is pure mind.

As it stands, however, this twofold conclusion not only lacks plausibility, but seems flatly self-contradictory. To say that mind and matter are not two different kinds of things but the same kind of thing, is not very plausible ; and it seems self-contradictory to say, either of mind or of matter, that it both is extended and is not extended in space. To tone down these defects is the chief rôle of Bergson's theory of memory. So far we have spoken as if perception or sensation were the only property of our minds; but obviously our mental life is composed of many other elements besides this. In addition to perceiving, we also, for instance, think and remember; and, as he observes, pure perception never occurs in practice, our perceptions being always mixed with memories to a greater or less extent. He brings this fact to bear on his theory about perception and matter in the following way. My mental life may vary from a state which contains almost nothing but perceptions, to one which contains almost nothing but memory. At one end of the scale is the state of things that occurs when I react to an imminent danger, as to a sudden blow threatening my eye. Here there is no memory, but a close approximation to pure perception; my mental life is narrowed down to a point and consists solely of a reflex action caused by my brain-process. But normally my mental life is immensely wider than the actions which correspond, point to point, with brain-process. At the other end of the scale is the diffused mental state which, when we . merely remember or are sunk in reverie, includes no perception of a present object; and, by a process which he describes as one of dilatation and contraction, our minds range through all the stages between these two extremes. Unless perception were mixed with memory, there would be no difference at all between perception and matter; and memory, in its pure state, would be mind unalloyed.

This statement of Bergson's views has, I hope, made at any rate this much clear—that his claim that common sense is on his side must not be taken too seriously. No doubt it is common sense to think that both minds and material objects are real; but we shall presently see reason to doubt whether he is entitled even to hold this. Meanwhile, nothing could well be less in accordance with common sense than his assertion that minds and material objects are more or less like one another, matter being not so completely extended, and mind not so completely unextended, as is generally supposed. For what he means by this is not that human minds take up some room, however little, that they are of some shape, and have some size, however small; he does not regard the soul, as it has sometimes been regarded in the past, as a small object composed of highly-refined matter. What he means is merely that, when I see a table, my consciousness of the table, far from being something different in kind from the table itself, is really the same kind of thing; there is only a difference of degree between them,

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