Objection 1. It would seem that the forms of bodies come from the angels. For Boethius says (De Trin. i): "From forms that are without matter come the forms that are in matter." But forms that are without matter are spiritual substances, and forms that are in matter are the forms of bodies. Therefore, the forms of bodies are from spiritual substances.
Objection 2. Further, all that is such by participation is reduced to that which is such by its essence. But spiritual substances are forms essentially, whereas corporeal creatures have forms by participation. Therefore the forms of corporeal things are derived from spiritual substances.
Objection 3. Further, spiritual substances have more power of causation than the heavenly bodies. But the heavenly bodies give form to things here below, for which reason they are said to cause generation and corruption. Much more, therefore, are material forms derived from spiritual substances.
On the contrary, Augustine says (De Trin. iii, 8): "We must not suppose that this corporeal matter serves the angels at their nod, but rather that it obeys God thus." But corporeal matter may be said thus to serve that from which it receives its form. Corporeal forms, then, are not from the angels, but from God.
I answer that, It was the opinion of some that all corporeal forms are derived from spiritual substances, which we call the angels. And there are two ways in which this has been stated. For Plato held that the forms of corporeal matter are derived from, and formed by, forms immaterially subsisting, by a kind of participation. Thus he held that there exists an immaterial man, and an immaterial horse, and so forth, and that from such the individual sensible things that we see are constituted, in so far as in corporeal matter there abides the impression received from these separate forms, by a kind of assimilation, or as he calls it, "participation" (Phaedo xlix). And, according to the Platonists, the order of forms corresponds to the order of those separate substances; for example, that there is a single separate substance, which is horse and the cause of all horses, whilst above this is separate life, or "per se" life, as they term it, which is the cause of all life, and that above this again is that which they call being itself, which is the cause of all being. Avicenna, however, and certain others, have maintained that the forms of corporeal things do not subsist "per se" in matter, but in the intellect only. Thus they say that from forms existing in the intellect of spiritual creatures (called "intelligences" by them, but "angels" by us) proceed all the forms of corporeal matter, as the form of his handiwork proceeds from the forms in the mind of the craftsman. This theory seems to be the same as that of certain heretics of modern times, who say that God indeed created all things, but that the devil formed corporeal matter, and differentiated it into species.
But all these opinions seem to have a common origin; they all, in fact, sought for a cause of forms as though the form were of itself brought into being. Whereas, as Aristotle (Metaph. vii, text. 26,27,28), proves, what is, properly speaking, made, is the "composite." Now, such are the forms of corruptible things that at one time they exist and at another exist not, without being themselves generated or corrupted, but by reason of the generation or corruption of the "composite"; since even forms have not being, but composites have being through forms: for, according to a thing's mode of being, is the mode in which it is brought into being. Since, then, like is produced from like, we must not look for the cause of corporeal forms in any immaterial form, but in something that is composite, as this fire is generated by that fire. Corporeal forms, therefore, are caused, not as emanations from some immaterial form, but by matter being brought from potentiality into act by some composite agent. But since the composite agent, which is a body, is moved by a created spiritual substance, as Augustine says (De Trin. iii, 4,5), it follows further that even corporeal forms are derived from spiritual substances, not emanating from them, but as the term of their movement. And, further still, the species of the angelic intellect, which are, as it were, the seminal types of corporeal forms, must be referred to God as the first cause. But in the first production of corporeal creatures no transmutation from potentiality to act can have taken place, and accordingly, the corporeal forms that bodies had when first produced came immediately form God, whose bidding alone matter obeys, as its own proper cause. To signify this, Moses prefaces each work with the words, "God said, Let this thing be," or "that," to denote the formation of all things by the Word of God, from Whom, according to Augustine [Tract. i. in Joan. and Gen. ad lit. i. 4, is "all form and fitness and concord of parts."
Reply to Objection 1. By immaterial forms Boethius understands the types of things in the mind of God. Thus the Apostle says (Hebrews 11:3): "By faith we understand that the world was framed by the Word of God; that from invisible things visible things might be made." But if by immaterial forms he understands the angels, we say that from them come material forms, not by emanation, but by motion.
Reply to Objection 2. Forms received into matter are to be referred, not to self-subsisting forms of the same type, as the Platonists held, but either to intelligible forms of the angelic intellect, from which they proceed by movement, or, still higher, to the types in the Divine intellect, by which the seeds of forms are implanted in created things, that they may be able to be brought by movement into act.
Reply to Objection 3. The heavenly bodies inform earthly ones by movement, not by emanation.
Source: Summa Theologica (New Advent)