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.

[21] 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?