_a._ The sensuous perceptible substance is that in which the matter is still distinguished from the efficient form. Hence this substance is finite; for the separation and externality of form and matter are precisely what constitute the nature of the finite. Sensuous substance, says Aristotle (Metaph. XII. 2), involves change, but in such a way that it passes over into the opposite; the opposites disappear in one another, and the third beyond these opposites, that which endures, the permanent in this change, is matter. Now the leading categories of change which Aristotle names are the four differences, in regard to the What (κατὰ τὸ τί), or in regard to quality (ποιόν), or in regard to quantity (ποσόν), or in regard to place where (ποῦ). The first change is the origination and decay of simple determinate Being (κατὰ τόδε); the second change is that of the further qualities (κατὰ τὸ πάθος); the third, increase and diminution; the fourth, motion. Matter is the dead substance on which take place the changes which matter passes through. “The change itself is from potential into actual existence; possible whiteness transforms itself into actual whiteness. Thus things do not arise casually out of nothing, but all arises out of what exists, though it exists only in potentiality, not in actuality.” The possible is thus really a general implicit existence, which brings about these determinations, without producing one out of the other. Matter is thus simple potentiality, which, however, is placed in opposition to itself, so that a thing in its actuality only becomes that which its matter was also in potentiality. There are thus three moments posited: matter, as the general substratum of change, neutral in respect of what is different (ἐξ οὗ); the opposed determinations of form, which are negative to each other as that which is to be abrogated and that which is to be posited (τι and εἴς τι); the first mover (ὑφ̓ οὗ), pure activity (Metaph. VII. 7; IX. 8; XII. 3).[89] But activity is the unity of form and matter; how these two are in the other, Aristotle does not, however, further explain. Thus in sensuous substance there appears the diversity of the moments, though not as yet their return into themselves; but activity is the negative which ideally contains in itself the opposite, therefore that also which is about to be.