12. It is the corporeal, then, that demands magnitude: the Ideal-Forms of body are Ideas installed in Mass.
But these Ideas enter, not into Magnitude itself but into some subject that has been brought to Magnitude. For to suppose them entering into Magnitude and not into Matter – is to represent them as being either without Magnitude and without Real-Existence (and therefore undistinguishable from the Matter) or not Ideal-Forms (apt to body) but Reason-Principles (utterly removed) whose sphere could only be Soul; at this, there would be no such thing as body (i.e., instead of Ideal-Forms shaping Matter and so producing body, there would be merely Reason-Principles dwelling remote in Soul.)
The multiplicity here must be based upon some unity which, since it has been brought to Magnitude, must be, itself, distinct from Magnitude. Matter is the base of Identity to all that is composite: once each of the constituents comes bringing its own Matter with it, there is no need of any other base. No doubt there must be a container, as it were a place, to receive what is to enter, but Matter and even body precede place and space; the primal necessity, in order to the existence of body, is Matter.
There is no force in the suggestion that, since production and act are immaterial, corporeal entities also must be immaterial.
Bodies are compound, actions not. Further, Matter does in some sense underlie action; it supplies the substratum to the doer: it is permanently within him though it does not enter as a constituent into the act where, indeed, it would be a hindrance. Doubtless, one act does not change into another – as would be the case if there were a specific Matter of actions – but the doer directs himself from one act to another so that he is the Matter, himself, to his varying actions.
Matter, in sum, is necessary to quality and to quantity, and, therefore, to body.
It is, thus, no name void of content; we know there is such a base, invisible and without bulk though it be.
If we reject it, we must by the same reasoning reject qualities and mass: for quality, or mass, or any such entity, taken by itself apart, might be said not to exist. But these do exist, though in an obscure existence: there is much less ground for rejecting Matter, however it lurk, discerned by none of the senses.
It eludes the eye, for it is utterly outside of colour: it is not heard, for it is no sound: it is no flavour or savour for nostrils or palate: can it, perhaps, be known to touch? No: for neither is it corporeal; and touch deals with body, which is known by being solid, fragile, soft, hard, moist, dry – all properties utterly lacking in Matter.
It is grasped only by a mental process, though that not an act of the intellective mind but a reasoning that finds no subject; and so it stands revealed as the spurious thing it has been called. No bodiliness belongs to it; bodiliness is itself a phase of Reason-Principle and so is something different from Matter, as Matter, therefore, from it: bodiliness already operative and so to speak made concrete would be body manifest and not Matter unelaborated.