Every agents does indeed act for an end, and never for nothing. For nothing is the absence of anything. There is no such thing as “random”.
1 The first thing that we must show, then, is that in acting every agent intends an end.
2 In the case of things which obviously act for an end we call that toward which the inclination of the agent tend the end. For, if it attain this, it is said to attain its end; but if it fail in regard to this, it fails in regard to the end intended, as is evident in the case of the physician working for the sake of health, and of the man who is running toward a set objective.
As far as this point is concerned, it makes no difference whether the being tending to an end is a knowing being or not. For, just as the target is the end for the archer, so is it the end for the motion of the arrow.
Now every inclination of an agent tends toward something definite. A given action does not stem from merely any power but heating comes from heat, cooling from cold. Thus it is that actions are specifically distinguished by virtue of diversity of active powers. In fact, an action may sometime terminate in something which is made, as building does in a house, and as healing does in health. Sometimes, however, it does not, as in the cases of understanding and sensing. Now, if an action does in fact terminate in some thing that is made, the inclination of the agent tend through the action toward the thing that is produced. But if it does not terminate in a product, then the inclination of the agent tends toward the action itself. So, it must be that every agent in acting intends an end, sometimes the action itself, sometimes a thing produced by the action.
Notes Insert What’s My Line about product joke here.
3 Again, with reference to all things that act for an end, we say that the ultimate end is that beyond which the agent seeks nothing else; thus, the action of a physician goes as far as health, but when it is attained there is no desire for anything further. Now, in the action of all agents, one may find something beyond which the agent seeks nothing further. Otherwise, actions would tend to infinity, which is impossible. Since “it is impossible to proceed to infinity,” the agent could not begin to act, because nothing is moved toward what cannot be reached. Therefore, every agent acts for an end.
Notes You can’t go to where you can’t get to, and don’t know where it is. Infinity is tricky, as the next argument shows. This even holds after the resurrection. Infinity is infinitely far away, always. Heaven, and the other place, can’t become boring.
4 Besides, if the actions of an agent are supposed to proceed to infinity, then there must be as a consequence to these actions either something that is produced, or nothing. Supposing that there is something that results, then the existence of this thing would come about after an infinite number of actions. But that which presupposes an infinite number of things cannot come into existence, since it is impossible to proceed to infinity. Now, that which is impossible in regard to being is impossible in regard to coming into being. And it is impossible to produce that which cannot come into being. Therefore, it is impossible for an agent to begin to produce something that presupposes an infinite number of actions.
Supposing, on the other hand, that nothing follows as a product of these actions, then the order of such actions must either depend on the ordering of the active powers (as in the case of a man who senses so that he may imagine, imagines so that he may understand, and then understands so that he may will); or it depends on the ordering of objects (thus, I think of body so that I may be able to think of soul, which latter I think so that I may be able to think of immaterial substance, which in turn I think so that I may be able to think about God).
Indeed, it is impossible to proceed to infinity, either through a series of active powers (for instance, through the forms of things, as is proved in Metaphysics [Ia, 2: 994a 1–b6], for the form is the principle of action) or through a series of objects (for there is not an infinite number of beings, because there is one First Being, as we demonstrated earlier [I:42]). So, it is not possible for actions to proceed to infinity. There must, then, be something which satisfies the agent’s desire when it is attained. Therefore, every agent acts for an end.
5 Moreover, for things which act for an end, all things intermediate between the first agent and the ultimate end are as ends in regard to things prior, and as active principles with regard to things consequent. So, if the agent’s desire is not directed to some definite thing, but, rather, the actions are multiplied to infinity, as was said, then the active principles must be multiplied to infinity. This is impossible, as we showed above. Therefore, the agent’s desire must be directed to some definite thing.
6 Furthermore, for every agent the principle of its action is either its nature or its intellect. Now, there is no question that intellectual agents act for the sake of an end, because they think ahead of time in their intellects of the things which they achieve through action; and their action stems from such preconception. This is what it means for intellect to be the principle of action.
Just as the entire likeness of the result achieved by the actions of an intelligent agent exists in the intellect that preconceives it, so, too, does the likeness of a natural resultant pre-exist in the natural agent; and as a consequence of this, the action is determined to a definite result. For fire gives rise to fire, and an olive to an olive. Therefore, the agent that acts with nature as its principle is just as much directed to a definite end, in its action, as is the agent that acts through intellect as its principle. Therefore, every agent acts for an end.
Notes Hello, free will!
7 Again, there is no fault to be found, except in the case of things that are for the sake of an end. A fault is never attributed to an agent, if the failure is related to something that is not the agent’s end. Thus, the fault of failing to heal is imputed to the physician, but not to the builder or the grammarian. We do find fault with things done according to art, for instance, when the grammarian does not speak correctly, and also in things done according to nature, as is evident in the case of the birth of monsters. Therefore, it is just as true of the agent that acts in accord with nature as of the agent who acts in accord with art and as a result of previous planning that action is for the sake of an end.
8 Besides, if an agent did not incline toward some definite effect, all results would be a matter of indifference for him. Now, he who looks upon a manifold number of things with indifference no more succeeds in doing one of them than another. Hence, from an agent contingently indifferent to alternatives no effect follows, unless he be determined to one effect by something. So, it would be impossible for him to act. Therefore, every agent tends toward some determinate effect, and this is called his end.
Notes Another way to put this is to think that the number of things you are not now doing is infinite. But you’ve picked one thing.
9 Of course, there are some actions that do not seem to be for an end. Examples are playful and contemplative actions, and those that are done without attention, like rubbing one’s beard and the like.
These examples could make a person think that there are some cases of acting without an end. However, we must understand that contemplative actions are not for another end, but are themselves ends. On the other hand, acts of play are sometimes ends, as in the case of a man who plays solely for the pleasure attaching to play; at other times they are for an end, for instance, when we play so that we can study better afterward. Actions that are done without attention do not stem from the intellect but from some sudden act of imagination or from a natural source. Thus, a disorder of the humors produces an itch and is the cause of rubbing the beard, and this is done without intellectual attention. So, these actions do tend to some end, though quite apart from the order of the intellect.
10 Through this consideration the error of the ancient natural philosophers is refuted; they claimed that all things come about as a result of material necessity, for they completely excluded final cause from things.