FIFTH PROOF: FROM THE ORDER PREVAILING IN THE UNIVERSE

We observe that irrational beings act for an end. Indeed, we notice that there is a wonderful order prevailing in the regular courses of the heavenly bodies. The centripetal and centrifugal forces are so regulated that the heavenly bodies move in their orbits with enormous speed and in perfect harmony. No less striking are the unity and variety which we behold in the organic structures of plants, animals, and man. Finality, or the relation to an end, is clearly seen in the evolution of an egg, which virtually contains a certain determined organism, and in the case of those organs which are adapted to certain very special functions, such as the eye, which is for seeing, and the ear, which is for hearing. Finally, we find the same to be the case with those animals which act by instinct, for instance, the bee, which builds its hive.

What particularly manifests this finality, as St. Thomas notes, is the fact that natural agents of the irrational order "always or nearly always act in the same way, and in a way designed to obtain that which best agrees with their nature," e. g., for their development, nutrition, reproduction, etc.

"We see things which lack intelligence, such as material bodies, act for an end, and this is evident from their acting always, or nearly always, in the same way, so as to obtain the best. Whence it is plain that they achieve their end not fortuitously, but designedly. Now, whatever lacks intelligence, cannot tend towards an end, unless it be directed by some being endowed with knowledge and intelligence; just as the arrow is shot to its mark by the archer. Therefore, some intelligent being exists, by whom all natural things are directed to their end; and this being we call God." (Ia, q. 2, a. 3).

This terminus of their action, precisely because it is something determinate and in complete conformity with their nature, is entitled to the name of end; for the end is the good in view of which an agent acts.

Moreover, even before the existence of God has been proved, the necessity and universality of the principle of finality are evident truths. The principle may be expressed by the following formula: "Every agent acts for an end." "Were it otherwise," says St. Thomas, "one thing would not follow from the action of the agent more than another, except by chance. . . . For the natural agent to produce an effect which is determinate, it must be determined for some particular effect, and this is what is meant by the word end."

Summa Theol., Ia, q. 44, a. 4; Ia IIae, q. 1, a. 2; C. Gentes, Bk. III, c. 2.

It will not do to have recourse to chance, for chance is an accidental cause (causa per accidens), and hence is not the cause of what happens always and according to nature. Otherwise, the accidental would no longer be accidental; instead of being something which accrues (accidit) to the essence, it would be its foundation, and in that ease the essential would be subordinate to the accidental, which is absurd. The wonderful order existing in the universe would be the result of no order, the greater would proceed from the less.

Neither will it do to appeal solely to the efficient cause, and to reject the final cause. For in that case we could not give any reason for the action of an agent: why, for instance, a certain organ has a certain determinate tendency; nor could we say why an agent acts instead of not acting. There would be no raison d'être for the action. The active potency or the inclination of the agent is not without a motive, called tendency, because it tends essentially towards something, just as the imperfect tends towards the perfect. "Potentia dicitur ad actum," potency essentially refers to act, or is essentially of the intentional order. For instance, the faculty of sight is expressly designed for seeing.

See Aristotle , Physics, Bk. II, c. 8 ff., and the Commentary of St. Thomas,  Lect. 7-14.

Therefore, we cannot doubt the existence of finality in the world, the wonderful order of which is nothing else but the suitable arrangement of means in view of an end (apta dispositio mediorum ad finem). The bird flies not only because it has wings (efficient cause), but the wings are for the purpose of flying (final cause). Otherwise, the particular formation of its wings would be without a sufficient reason. To affirm that anything is without a sufficient reason, is to formulate a proposition which is unintelligible and absurd (see supra, n. 24). St. Thomas would have said: "It would be foolish to make such an assertion," just as he said that "David of Dinant foolishly declared God to be prime matter."

Summa Theol., Ia, q. 3, a, 8.

Now, irrational beings cannot tend towards an end, unless they are directed by an intelligence, as the arrow is shot to the mark by the archer. In fact, one thing cannot be directed to another, unless there be a directing cause, which must, of necessity, be intelligent, for, "sapientis est ordinare." Why? Because an intelligent being alone perceives the raison d'être of things, and the end is the raison d'être of the means. "Irrational beings," says St. Thomas, "tend towards an end by natural inclination; they are, as it were, moved by another and not by themselves, since they have no knowledge of the end as such."

Ia IIae, q. 1, a. 2.

There is, therefore, a supreme intelligent Being, who directs all things to their respective ends. It will not do to say that the universal Designer has, like ourselves, an intellectual faculty directed to intelligible being, but what is demanded is a designing intelligence of a higher order. The supreme Designer cannot be designed for any other purpose. He must be Thought itself, self-subsisting Intellection, just as he is self-subsisting Being: "ipsum intelligere subsistens."

Ia, q. 3, a. 4; q. 14, a. 1 and 4.