Objection 1. It would seem that primary matter is not created by God. For whatever is made is composed of a subject and of something else (Phys. i, text 62). But primary matter has no subject. Therefore primary matter cannot have been made by God.
Objection 2. Further, action and passion are opposite members of a division. But as the first active principle is God, so the first passive principle is matter. Therefore God and primary matter are two principles divided against each other, neither of which is from the other.
Objection 3. Further, every agent produces its like, and thus, since every agent acts in proportion to its actuality, it follows that everything made is in some degree actual. But primary matter is only in potentiality, formally considered in itself. Therefore it is against the nature of primary matter to be a thing made.
On the contrary, Augustine says (Confess. xii, 7), Two "things hast Thou made, O Lord; one nigh unto Thyself"--viz. angels--"the other nigh unto nothing"--viz. primary matter.
I answer that, The ancient philosophers gradually, and as it were step by step, advanced to the knowledge of truth. At first being of grosser mind, they failed to realize that any beings existed except sensible bodies. And those among them who admitted movement, did not consider it except as regards certain accidents, for instance, in relation to rarefaction and condensation, by union and separation. And supposing as they did that corporeal substance itself was uncreated, they assigned certain causes for these accidental changes, as for instance, affinity, discord, intellect, or something of that kind. An advance was made when they understood that there was a distinction between the substantial form and matter, which latter they imagined to be uncreated, and when they perceived transmutation to take place in bodies in regard to essential forms. Such transmutations they attributed to certain universal causes, such as the oblique circle [The zodiac], according to Aristotle (De Gener. ii), or ideas, according to Plato. But we must take into consideration that matter is contracted by its form to a determinate species, as a substance, belonging to a certain species, is contracted by a supervening accident to a determinate mode of being; for instance, man by whiteness. Each of these opinions, therefore, considered "being" under some particular aspect, either as "this" or as "such"; and so they assigned particular efficient causes to things. Then others there were who arose to the consideration of "being," as being, and who assigned a cause to things, not as "these," or as "such," but as "beings."
Therefore whatever is the cause of things considered as beings, must be the cause of things, not only according as they are "such" by accidental forms, nor according as they are "these" by substantial forms, but also according to all that belongs to their being at all in any way. And thus it is necessary to say that also primary matter is created by the universal cause of things.
Reply to Objection 1. The Philosopher (Phys. i, text 62), is speaking of "becoming" in particular--that is, from form to form, either accidental or substantial. But here we are speaking of things according to their emanation from the universal principle of being; from which emanation matter itself is not excluded, although it is excluded from the former mode of being made.
Reply to Objection 2. Passion is an effect of action. Hence it is reasonable that the first passive principle should be the effect of the first active principle, since every imperfect thing is caused by one perfect. For the first principle must be most perfect, as Aristotle says (Metaph. xii, text 40).
Reply to Objection 3. The reason adduced does not show that matter is not created, but that it is not created without form; for though everything created is actual, still it is not pure act. Hence it is necessary that even what is potential in it should be created, if all that belongs to its being is created.
Source: Summa Theologica (New Advent)