12. This is Plato's conception: to him participation does not, in the case of Matter, comport any such presence of an Ideal-form in a Substance to be shaped by it as would produce one compound thing made up of the two elements changing at the same moment, merging into one another, modified each by the other.
In his haste to his purpose he raises many difficult questions, but he is determined to disown that view; he labours to indicate in what mode Matter can receive the Ideal-forms without being, itself, modified. The direct way is debarred since it is not easy to point to things actually present in a base and yet leaving that base unaffected: he therefore devises a metaphor for participation without modification, one which supports, also, his thesis that all appearing to the senses is void of substantial existence and that the region of mere seeming is vast.
Holding, as he does, that it is the patterns displayed upon Matter that cause all experience in living bodies while the Matter itself remains unaffected, he chooses this way of stating its immutability, leaving us to make out for ourselves that those very patterns impressed upon it do not comport any experience, any modification, in itself.
In the case, no doubt, of the living bodies that take one pattern or shape after having borne another, it might be said that there was a change, the variation of shape being made verbally equivalent to a real change: but since Matter is essentially without shape or magnitude, the appearing of shape upon it can by no freedom of phrase be described as a change within it. On this point one must have "a rule for thick and thin" one may safely say that the underlying Kind contains nothing whatever in the mode commonly supposed.
But if we reject even the idea of its really containing at least the patterns upon it, how is it, in any sense, a recipient?
The answer is that in the metaphor cited we have some reasonably adequate indication of the impassibility of Matter coupled with the presence upon it of what may be described as images of things not present.
But we cannot leave the point of its impassibility without a warning against allowing ourselves to be deluded by sheer custom of speech.
Plato speaks of Matter as becoming dry, wet, inflamed, but we must remember the words that follow: "and taking the shape of air and of water": this blunts the expressions "becoming wet, becoming inflamed"; once we have Matter thus admitting these shapes, we learn that it has not itself become a shaped thing but that the shapes remain distinct as they entered. We see, further, that the expression "becoming inflamed" is not to be taken strictly: it is rather a case of becoming fire. Becoming fire is very different from becoming inflamed, which implies an outside agency and, therefore, susceptibility to modification. Matter, being itself a portion of fire, cannot be said to catch fire. To suggest that the fire not merely permeates the matter, but actually sets it on fire is like saying that a statue permeates its bronze.
Further, if what enters must be an Ideal-Principle how could it set Matter aflame? But what if it is a pattern or condition? No: the object set aflame is so in virtue of the combination of Matter and condition.
But how can this follow on the conjunction when no unity has been produced by the two?
Even if such a unity had been produced, it would be a unity of things not mutually sharing experiences but acting upon each other. And the question would then arise whether each was effective upon the other or whether the sole action was not that of one (the form) preventing the other [the Matter] from slipping away?
But when any material thing is severed, must not the Matter be divided with it? Surely the bodily modification and other experience that have accompanied the sundering, must have occurred, identically, within the Matter?
This reasoning would force the destructibility of Matter upon us: "the body is dissolved; then the Matter is dissolved." We would have to allow Matter to be a thing of quantity, a magnitude. But since it is not a magnitude it could not have the experiences that belong to magnitude and, on the larger scale, since it is not body it cannot know the experiences of body.
In fact those that declare Matter subject to modification may as well declare it body right out.