From a purely practical point of view the much derided pineal gland theory would serve. If we could be content to view Descartes as a man who wanted to make the world safe for physical science, then there would be a good deal to be said for his doctrine. In the old philosophy exact science had been frustrated by the hypothesis of loose relations all over the field of nature. Descartes had cleared them from as much of the field as science was then in a position to investigate; he allowed only one such relation to subsist, the one which experience appeared unmistakably to force upon us—that between our own mind and its bodily vehicle. He had exorcized the spirits from the rest of nature; and though there was a spirit here which could not be exorcized, the philosophic conjurer had nevertheless confined it and its unaccountable pranks within a minutely narrow magic circle: all mind could do was to turn the one tiny switch at the centre of its animal telephone system. It could create no energy—it could merely redirect the currents actually flowing.
Practically this might do, but speculatively it was most disturbing. For if the 'loose relation' had to be admitted in one instance, it was admitted in principle; and one could not get rid of the suspicion that it would turn up elsewhere, and that the banishment of it from every other field represented a convenient pragmatic postulate rather than a solid metaphysical truth. Moreover, the correlation of the unitary soul with the unitary gland might do justice to a mechanistical philosophy, but it did not do justice to the soul's own consciousness of itself. The soul's consciousness is the 'idea' or 'representation' of the life of the whole body, certainly not of the life of the pineal gland nor, as the unreflective nowadays would say, of the brain. I am not conscious in, or of, my brain except when I have a headache; consciousness is in my eyes and finger-tips and so on. It is physically true, no doubt, that consciousness in and of my finger-tips is not possible without the functioning of my brain; but that is a poor reason for locating the consciousness in the brain. The filament of the electric bulb will not be incandescent apart from the functioning of the dynamo; but that is a poor reason for saying that the incandescence is in the dynamo.
Certainly the area of representation in our mind is not simply equivalent to the area of our body. But in so far as the confines of mental representation part company with the confines of the body, it is not that they may contract and fall back upon the pineal gland, but that they may expand and advance over the surrounding world. The mind does not represent its own body merely, it represents the world in so far as the world affects that body or is physically reproduced in it. The mind has no observable natural relation to the pineal gland. It has only two natural relations: to its body as a whole and to its effective environment. What Descartes had really done was to pretend that the soul was related to the pineal gland as it is in fact related to its whole body; and then that it was related to the bodily members as in fact it is related to outer environment. The members became an inner environment, known only in so far as they affected the pineal gland; just as the outer environment in its turn was to be known only in so far as it affected the members.
This doctrine of a double environment was wholly artificial. It was forced on Descartes by the requirements of mechanistical science: if the members were simply a plurality of things, they must really be parts of environment; the body which the soul indwelt must be a body; presumably, then, the pineal gland. An untenable compromise, surely, between admitting and denying the reality of the soul's incarnation.
What, then, was to be done? Descartes's rivals and successors attempted several solutions, which it would be too long to examine here. They dissatisfied Leibniz and they have certainly no less dissatisfied posterity. It will be enough for us here to consider what Leibniz did. He admitted, to begin with, the psychological fact. The unity of consciousness is the representation of a plurality—the plurality of the members, and through them the plurality of the world. Here, surely, was the very principle the new philosophy needed for the reconciliation of substantial unity with mechanical plurality of parts. For it is directly evident to us that consciousness focuses the plurality of environing things in a unity of representation. This is no philosophical theory, it is a simple fact. Our body, then, as a physical system is a mechanical plurality; as focused in consciousness it is a unity of 'idea'.
Very well: but we have not got far yet. For the old difficulty still remains—it is purely arbitrary, after all, that a unitary consciousness should be attached to, and represent, a mechanical collection of things which happen to interact in a sort of pattern. If there is a consciousness attached to human bodies, then why not to systems of clockwork? If the body is represented as unity, it must surely be because it is unity, as the old philosophy had held. But how can we reintroduce unity into the body without reintroducing substantial form, and destroying the mechanistical plurality which the new science demanded?
It is at this point that Leibniz produces the speculative postulate of his system. Why not reverse the relation, and make the members represent the mind as the mind represents the members? For then the unity of person represented in the mind will become something actual in the members also.
Representation appears to common sense to be a one-way sort of traffic. If my mind represents my bodily members, something happens to my mind, for it becomes a representation of such members in such a state; but nothing happens to the members by their being so represented in the mind. The mental representation obeys the bodily facts; the bodily facts do not obey the mental representation. It seems nonsense to say that my members obey my mind because they are mirrored in it. And yet my members do obey my mind, or at least common sense supposes so. Sometimes my mind, instead of representing the state my members are in, represents a state which it intends that they shall be in, for example, that my hand should go through the motion of writing these words. And my hand obeys; its action becomes the moving diagram of my thought, my thought is represented or expressed in the manual act. Here the relation of mind and members appears to be reversed: instead of its representing them, they represent it. With this representation it is the opposite of what it was with the other. By the members' being represented in the mind, something happened to the mind, and nothing to the members; by the mind's being represented in the members something happens to the members and nothing to the mind.
Why should not we take this seriously? Why not allow that there is two-way traffic—by one relation the mind represents the members, by another the members represent the mind? But then again, how can we take it seriously? For representation, in the required sense, is a mental act; brute matter can represent nothing, only mind can represent. And the members are brute matter. But are they? How do we know that? By brute matter we understand extended lumps of stuff, interacting with one another mechanically, as do, for example, two cogs in a piece of clockwork. But this is a large-scale view. The cogs are themselves composed of interrelated parts and those parts of others, and so on ad infinitum. Who knows what the ultimate constituents really are? The 'modern' philosophers, certainly, have proposed no hypothesis about them which even looks like making sense. They have supposed that the apparently inert lumps, the cogs, are composed of parts themselves equally inert, and that by subdivision we shall still reach nothing but the inert. But this supposition is in flat contradiction with what physical theory demands. We have to allow the reality of force in physics. Now the force which large-scale bodies display may easily be the block-effect of activity in their minute real constituents. If not, where does it come from? Let it be supposed, then, that these minute real constituents are active because they are alive, because they are minds; for indeed we have no notion of activity other than the perception we have of our own. We have no notion of it except as something mental. On the hypothesis that the constituents of active body are also mental, this limitation in our conception of activity need cause us neither sorrow nor surprise.
The mind-units which make up body will not of course be developed and fully conscious minds like yours or mine, and it is only for want of a better word that we call them minds at all. They will