I answer that, Every effect in some degree represents its cause, but diversely. For some effects represent only the causality of the cause, but not its form; as smoke represents fire. Such a representation is called a "trace": for a trace shows that someone has passed by but not who it is. Other effects represent the cause as regards the similitude of its form, as fire generated represents fire generating; and a statue of Mercury represents Mercury; and this is called the representation of "image." Now the processions of the divine Persons are referred to the acts of intellect and will, as was said above (Q[27]). For the Son proceeds as the word of the intellect; and the Holy Ghost proceeds as love of the will. Therefore in rational creatures, possessing intellect and will, there is found the representation of the Trinity by way of image, inasmuch as there is found in them the word conceived, and the love proceeding.
But in all creatures there is found the trace of the Trinity, inasmuch as in every creature are found some things which are necessarily reduced to the divine Persons as to their cause. For every creature subsists in its own being, and has a form, whereby it is determined to a species, and has relation to something else. Therefore as it is a created substance, it represents the cause and principle; and so in that manner it shows the Person of the Father, Who is the "principle from no principle." According as it has a form and species, it represents the Word as the form of the thing made by art is from the conception of the craftsman. According as it has relation of order, it represents the Holy Ghost, inasmuch as He is love, because the order of the effect to something else is from the will of the Creator. And therefore Augustine says (De Trin. vi 10) that the trace of the Trinity is found in every creature, according "as it is one individual," and according "as it is formed by a species," and according as it "has a certain relation of order." And to these also are reduced those three, "number," "weight," and "measure," mentioned in the Book of Wisdom (9:21). For "measure" refers to the substance of the thing limited by its principles, "number" refers to the species, "weight" refers to the order. And to these three are reduced the other three mentioned by Augustine (De Nat. Boni iii), "mode," "species," and "order," and also those he mentions (QQ. 83, qu. 18): "that which exists; whereby it is distinguished; whereby it agrees." For a thing exists by its substance, is distinct by its form, and agrees by its order. Other similar expressions may be easily reduced to the above.
Reply to Objection 1: The representation of the trace is to be referred to the appropriations: in which manner we are able to arrive at a knowledge of the trinity of the divine persons from creatures, as we have said (Q[32], A[1]).
Reply to Objection 2: A creature properly speaking is a thing self-subsisting; and in such are the three above-mentioned things to be found. Nor is it necessary that these three things should be found in all that exists in the creature; but only to a subsisting being is the trace ascribed in regard to those three things.
Reply to Objection 3: The processions of the persons are also in some way the cause and type of creation; as appears from the above (A[6]).
Whether creation is mingled with works of nature and art?
Objection 1: It would seem that creation is mingled in works of nature and art. For in every operation of nature and art some form is produced. But it is not produced from anything, since matter has no part in it. Therefore it is produced from nothing; and thus in every operation of nature and art there is creation.
Objection 2: Further, the effect is not more powerful than its cause. But in natural things the only agent is the accidental form, which is an active or a passive form. Therefore the substantial form is not produced by the operation of nature; and therefore it must be produced by creation.
Objection 3: Further, in nature like begets like. But some things are found generated in nature by a thing unlike to them; as is evident in animals generated through putrefaction. Therefore the form of these is not from nature, but by creation; and the same reason applies to other things.
Objection 4: Further, what is not created, is not a creature. If therefore in nature's productions there were not creation, it would follow that nature's productions are not creatures; which is heretical.
On the contrary, Augustine (Super Gen. v, 6,14,15) distinguishes the work of propagation, which is a work of nature, from the work of creation.
I answer that, The doubt on this subject arises from the forms which, some said, do not come into existence by the action of nature, but previously exist in matter; for they asserted that forms are latent. This arose from ignorance concerning matter, and from not knowing how to distinguish between potentiality and act. For because forms pre-exist in matter, "in potentiality," they asserted that they pre-exist "simply." Others, however, said that the forms were given or caused by a separate agent by way of creation; and accordingly, that to each operation of nature is joined creation. But this opinion arose from ignorance concerning form. For they failed to consider that the form of the natural body is not subsisting, but is that by which a thing is. And therefore, since to be made and to be created belong properly to a subsisting thing alone, as shown above (A[4]), it does not belong to forms to be made or to be created, but to be "concreated." What, indeed, is properly made by the natural agent is the "composite," which is made from matter.
Hence in the works of nature creation does not enter, but is presupposed to the work of nature.
Reply to Objection 1: Forms begin to be actual when the composite things are made, not as though they were made "directly," but only "indirectly."
Reply to Objection 2: The active qualities in nature act by virtue of substantial forms: and therefore the natural agent not only produces its like according to quality, but according to species.
Reply to Objection 3: For the generation of imperfect animals, a universal agent suffices, and this is to be found in the celestial power to which they are assimilated, not in species, but according to a kind of analogy. Nor is it necessary to say that their forms are created by a separate agent. However, for the generation of perfect animals the universal agent does not suffice, but a proper agent is required, in the shape of a univocal generator.
Reply to Objection 4: The operation of nature takes place only on the presupposition of created principles; and thus the products of nature are called creatures.