Objection 1. It would seem that there are no seminal virtues in corporeal matter. For virtue [ratio] implies something of a spiritual order. But in corporeal matter nothing exists spiritually, but only materially, that is, according to the mode of that in which it is. Therefore there are no seminal virtues in corporeal matter.
Objection 2. Further, Augustine (De Trin. iii, 8,9) says that demons produce certain results by employing with a hidden movement certain seeds, which they know to exist in matter. But bodies, not virtues, can be employed with local movement. Therefore it is unreasonable to say that there are seminal virtues in corporeal matter.
Objection 3. Further, seeds are active principles. But there are no active principles in corporeal matter; since, as we have said above, matter is not competent to act (1, ad 2,4). Therefore there are no seminal virtues in corporeal matter.
Objection 4. Further, there are said to be certain "causal virtues" (Augustine, De Gen. ad lit. v, 4) which seem to suffice for the production of things. But seminal virtues are not causal virtues: for miracles are outside the scope of seminal virtues, but not of causal virtues. Therefore it is unreasonable to say that there are seminal virtues in corporeal matter.
On the contrary, Augustine says (De Trin. iii, 8): "Of all the things which are generated in a corporeal and visible fashion, certain seeds lie hidden in the corporeal things of this world."
I answer that, It is customary to name things after what is more perfect, as the Philosopher says (De Anima ii, 4). Now in the whole corporeal nature, living bodies are the most perfect: wherefore the word "nature" has been transferred from living things to all natural things. For the word itself, "nature," as the Philosopher says (Metaph. v, Did. iv, 4), was first applied to signify the generation of living things, which is called "nativity": and because living things are generated from a principle united to them, as fruit from a tree, and the offspring from the mother, to whom it is united, consequently the word "nature" has been applied to every principle of movement existing in that which is moved. Now it is manifest that the active and passive principles of the generation of living things are the seeds from which living things are generated. Therefore Augustine fittingly gave the name of "seminal virtues" [seminales rationes] to all those active and passive virtues which are the principles of natural generation and movement.
These active and passive virtues may be considered in several orders. For in the first place, as Augustine says (Gen. ad lit. vi, 10), they are principally and originally in the Word of God, as "typal ideas."
Secondly, they are in the elements of the world, where they were produced altogether at the beginning, as in "universal causes."
Thirdly, they are in those things which, in the succession of time, are produced by universal causes, for instance in this plant, and in that animal, as in "particular causes."
Fourthly, they are in the "seeds" produced from animals and plants. And these again are compared to further particular effects, as the primordial universal causes to the first effects produced.
Reply to Objection 1. These active and passive virtues of natural things, thought not called "virtues" [rationes] by reason of their being in corporeal matter, can nevertheless be so called in respect of their origin, forasmuch as they are the effect of the typal ideas [rationes ideales].
Reply to Objection 2. These active and passive virtues are in certain parts of corporeal things: and when they are employed with local movement for the production of certain results, we speak of the demons as employing seeds.
Reply to Objection 3. The seed of the male is the active principle in the generation of an animal. But that can be called seed also which the female contributes as the passive principle. And thus the word "seed" covers both active and passive principles.
Reply to Objection 4. From the words of Augustine when speaking of these seminal virtues, it is easy to gather that they are also causal virtues, just as seed is a kind of cause: for he says (De Trin. iii, 9) that, "as a mother is pregnant with the unborn offspring, so is the world itself pregnant with the causes of unborn things." Nevertheless, the "typal ideas" can be called "causal virtues," but not, strictly speaking, "seminal virtues," because seed is not a separate principle; and because miracles are not wrought outside the scope of causal virtues. Likewise neither are miracles wrought outside the scope of the passive virtues so implanted in the creature, that the latter can be used to any purpose that God commands. But miracles are said to be wrought outside the scope of the natural active virtues, and the passive potentialities which are ordered to such active virtues, and this is what is meant when we say that they are wrought outside the scope of seminal virtues.
Source: Summa Theologica (New Advent)