Enneads III.6: Of the Impassibility of Incorporeal Entities (Soul and and Matter)
Sense-objects Are Unreal and Are Chiefly Made Up of Appearance
12. Plato[66] agreed with this, and being persuaded that, by participation, matter does not receive form and shape, as would some substrate that should constitute a composite of things intimately united by their transformation, their mixture, and their common affections; in order to demonstrate the opposite, namely, that matter remains impassible while receiving forms, invented a most apposite illustration of a participation that operates without anything being affected (namely, that engravers, before using dies on the soft wax, clean them carefully). Almost any other kind of illustration would fail to explain how the substrate can remain the same in the presence of forms. While trying to achieve his purpose, Plato has raised many questions; he has besides applied himself to demonstrate that sense-objects are devoid of reality, and that a large part of their hypostatic substance is constituted by appearance. Plato demonstrates the permanence and identity of matter by showing that it is by the figures with which it is endued that matter affects animated bodies, without itself suffering any of their affections. He wishes to convince us that in being endued with these figures, matter undergoes neither affection nor alteration. Indeed, in the bodies that successively assume different figures, we may, relying on analogy, call the change of figures an alteration; but since matter has neither figure nor existence,[67] how could we, even by analogy, call the presence of a figure an alteration? The only sure way of avoiding a misunderstanding in expression is to say that the substrate possesses nothing in the manner it is usually supposed to possess it. How then could it possess the things it contains, unless as a figure? Plato's illustration means that matter is impassible, and that it contains the apparent presence of images which are not really present therein.
PLATO'S FIGURATIVE LANGUAGE MIGHT LEAD TO ERRORS ABOUT HIS REAL OPINIONS.
We must still further preliminarily insist on the impassibility of matter; for by using the usual terms we might be misled into wrongly thinking that matter could be affected. Thus Plato speaks[68] of matter being set on fire, being wetted, and so forth, as if it received the shapes of air or water. However, Plato modifies the statement that "matter receives the shapes of air and water" by the statement that matter "is set on fire and wetted," and he demonstrates that by receiving these shapes it nevertheless has none of its own, and that forms do not more than enter into it. This expression "matter is set on fire" must not be taken literally; it means only that matter becomes fire. Now to become fire is not the same thing as being set on fire; to be set on fire can achieve no more than what is different from fire, than what can be affected; for that which itself is a part of fire could not be set on fire. To insist on the opposite would amount to saying that metal itself formed a statue, or that fire itself spread into matter and set it on fire. The theory that a ("seminal) reason" had approached matter, forces us to question how this reason could have set matter on fire. The theory that a figure had approached matter would imply that that which is set on fire is already composed of two things (matter and a figure), and that these two entities form a single one. Although these two things would form a single one, they would not affect each other, and would act only on other entities. Nor would they even in this case act jointly; for one would effect no more than to hinder the other from avoiding (form). The theory that when the body is divided matter also must be divided, would have to answer the question, How could matter on being divided, escape the affection undergone by the composite (of form and matter)? On such a theory, one might even assert that matter was destroyed, and ask, Since the body is destroyed, why should not matter also be destroyed? What is affected and divided must be a quantity or magnitude. What is not a magnitude cannot experience the same modifications as a body. Therefore those who consider matter affectible would be forced to call it a body.