9. In answer: It must, first, be noted that there are a variety of modes in which an object may be said to be present to another or to exist in another. There is a "presence" which acts by changing the object- for good or for ill- as we see in the case of bodies, especially where there is life. But there is also a "presence" which acts, towards good or ill, with no modification of the object, as we have indicated in the case of the Soul. Then there is the case represented by the stamping of a design upon wax, where the "presence" of the added pattern causes no modification in the substance nor does its obliteration diminish it. And there is the example of Light whose presence does not even bring change of pattern to the object illuminated. A stone becoming cold does not change its nature in the process; it remains the stone it was. A drawing does not cease to be a drawing for being coloured.
The intermediary mass on which these surface changes appear is certainly not transmuted by them; but might there not be a modification of the underlying Matter?
No: it is impossible to think of Matter being modified by, for instance, colour- for, of course we must not talk of modification when there is no more than a presence, or at most a presenting of shape.
Mirrors and transparent objects, even more, offer a close parallel; they are quite unaffected by what is seen in or through them: material things are reflections, and the Matter on which they appear is further from being affected than is a mirror. Heat and cold are present in Matter, but the Matter itself suffers no change of temperature: growing hot and growing cold have to do only with quality; a quality enters and brings the impassible Substance under a new state- though, by the way, research into nature may show that cold is nothing positive but an absence, a mere negation. The qualities come together into Matter, but in most cases they can have no action upon each other; certainly there can be none between those of unlike scope: what effect, for example, could fragrance have on sweetness or the colour-quality on the quality of form, any quality on another of some unrelated order? The illustration of the mirror may well indicate to us that a given substratum may contain something quite distinct from itself- even something standing to it as a direct contrary- and yet remain entirely unaffected by what is thus present to it or merged into it.
A thing can be hurt only by something related to it, and similarly things are not changed or modified by any chance presence: modification comes by contrary acting upon contrary; things merely different leave each other as they were. Such modification by a direct contrary can obviously not occur in an order of things to which there is no contrary: Matter, therefore [the mere absence of Reality] cannot be modified: any modification that takes place can occur only in some compound of Matter and reality, or, speaking generally, in some agglomeration of actual things. The Matter itself- isolated, quite apart from all else, utterly simplex- must remain immune, untouched in the midst of all the interacting agencies; just as when people fight within their four walls, the house and the air in it remain without part in the turmoil.
We may take it, then, that while all the qualities and entities that appear upon Matter group to produce each the effect belonging to its nature, yet Matter itself remains immune, even more definitely immune than any of those qualities entering into it which, not being contraries, are not affected by each other.