Thomas Aquinas, On the Mutual Order of Things in a Created World

It can be shown from the foregoing that the last thing through which any real being is ordered to its end is its operation. Yet this is done in various ways, depending on the diversity of operations.

One kind of operation pertains to a thing as the mover of another, as in the actions of heating or sawing. Another is the operation of a thing that is moved by another, as in the case of being heated or being sawed. Still another operation is the perfection of an actually existing agent which does not tend to produce a change in another thing. And these last differ, first of all, from passion and motion, and secondly from action transitively productive of change in exterior matter. Examples of operations in this third sense are understanding, sensing, and willing. Hence, it is clear that the things which are moved, or passively worked on only, without actively moving or doing anything, tend to the divine likeness by being perfected within themselves; while the things that actively make and move, by virtue of their character, tend toward the divine likeness by being the causes of others. Finally, the things that move as a result of being moved tend toward the divine likeness in both ways.

Lower bodies, inasmuch as they are moved in their natural motions, are considered as moved things only, and not as movers, except in the accidental sense, for it may happen that a falling stone will put in motion a thing that gets in its way. And the same applies to alteration and the other kinds of change. Hence, the end of their motion is to achieve the divine likeness by being perfected in themselves; for instance, by possessing their proper form and being in their proper place.

On the other hand, celestial bodies move because they are moved. Hence, the end of their motion is to attain the divine likeness in both ways. In regard to the way which involves its own perfection, the celestial body comes to be in a certain place actually, to which place it was previously in potency. Nor does it achieve its perfection any less because it now stands in potency to the place in which it was previously. For, in the same way, prime matter tends toward its perfection by actually acquiring a form to which it was previously in. potency, even though it then ceases to have the other form which it actually possessed before, for this is the way that matter may receive in succession all the forms to which it is potential, so that its entire potentiality may be successively reduced to act, which could not be done all at once. Hence, since a celestial body is in potency to place in the same way that prime matter is to form, it achieves its perfection through the fact that its entire potency to place is successively reduced to act, which could not be done all at once.

In regard to the way which involves movers that actively move, the end of their motion is to attain the divine likeness by being the causes of others. Now, they are the causes of others by the fact that they cause generation and corruption and other changes in these lower things. So, the motions of the celestial bodies, as actively moving, are ordered to the generation and corruption which take Place in these lower bodies.-Nor is it unfitting that celestial bodies should move for the sake of the generation and corruption of these lower things, even though lower bodies are of less value than celestial bodies, while, of course, the end should be more important than what is for the sake of the end.

Indeed, the generating agent acts for the sake of the form of the product of generation, yet this product is not more valuable than the agent; rather, in the case of univocal agents it is of the same species as the agent. In fact, the generating agent intends as its ultimate end, not the form of the product generated, which is the end of the process of generation, but the likeness of divine being in the perpetuation of the species and in the diffusion of its goodness, through the act of handing on its specific form to others, and of being the cause of others. Similarly, then, celestial bodies, although they are of greater value than lower bodies, tend toward the generation of these latter, and through their motions to the actual eduction of the forms of the products of generation, not as an ultimate end but as thereby intending the divine likeness as an ultimate end, inasmuch as they exist as the causes of other things.

Now, we should keep in mind that a thing participates in the likeness of the divine will, through which things are brought into being and preserved, to the extent that it participates in the likeness of divine goodness which is the object of His will. Higher things participate more simply and more universally in the likeness of divine goodness, while lower things do so more particularly and more in detail. Hence, between celestial and lower bodies the likeness is not observed according to complete equivalence, as it is in the case of things of one kind. Rather, it is like the similarity of a universal agent to a particular effect. Therefore, just as in the order of lower bodies the intention of a particular agent is focused on the good of this species or that, so is the intention of a celestial body directed to the common good of corporeal substance which is preserved, and multiplied, and increased through generation.

As we said, since any moved thing, inasmuch as it is moved, tends to the divine likeness so that it may be perfected in itself, and since a thing is perfect in so far as it is actualized, the intention of everything existing in potency must be to tend through motion toward actuality. And so, the more posterior and more perfect an act is, the more fundamentally is the inclination of matter directed toward it. Hence. in regard to the last and most perfect act that matter can attain, the inclination of matter whereby it desires form must be inclined as toward the ultimate end of generation. Now, among the acts pertaining to forms, certain gradations are found. Thus, prime matter is in potency, first of all, to the form of an element. When it is existing under the form of an element it is in potency to the form of a mixed body; that is why the elements are matter for the mixed body. Considered under the form of a mixed body, it is in potency to a vegetative soul, for this sort of soul is the act of a body. In turn, the vegetative soul is in potency to a sensitive soul, and a sensitive one to an intellectual one. This the process of generation shows: at the start of generation there is the embryo living with plant life, later with animal life, and finally with human life. After this last type of form, no later and more noble form is found in the order of generable and corruptible things. Therefore, the ultimate end of the whole process of generation is the human soul, and matter tends toward it as toward an ultimate form. So, elements exist for the sake of mixed bodies; these latter exist for the sake of living bodies, among which plants exist for animals, and animals for men. Therefore, man is the end of the whole order of generation.

And since a thing is generated and preserved in being by the same reality, there is also an order in the preservation of things, which parallels the foregoing order of generation. Thus we see that mixed bodies are sustained by the appropriate qualities of the elements; plants, in turn, are nourished by mixed bodies; animals get their nourishment from plants: so, those that are more perfect and more powerful from those that are more imperfect and weaker. In fact, man uses all kinds of things for his own advantage: some for food, others for clothing. That is why handwas created nude by nature, since he is able to make clothes for, himself from other things; just as nature also provided him with no appropriate nourishment, except milk, because he can obtain food for himself from a variety of things. Other things handuses for transportation, since we find man the inferior of many animals in quickness of movement, and in the strength to do work; other animals being provided, as it were, for his assistance. And, in addition to this, man uses all sense objects for the perfection of intellectual knowledge. Hence it is said of man in the Psalms (8:8) in a statement directed to God: “Thou bast subjected all things under his feet.” And Aristotle says, in the Politics I [5: 1254b 9], that man has natural dominion over all animals.

So, if the motion of the heavens is ordered to generation, and if the whole of generation is ordered to man as a last end within this genus, it is clear that the end of celestial motion is ordered to man, as to an ultimate end in the genus of generable and mobile beings.

from Summa contra Gentiles, Book III, ch. 22, “Providence”, vol. 3 (Notre Dame (IN): University of Notre Dame Press, 1975), translated by Vernon J. Bourke, pp. 83-87.