Thomas Aquinas: Summa Theologica, Part I-II (Prima Secundae)

Since, as Damascene states (De Fide Orth. ii, 12), man is said to be made in God's image, in so far as the image implies "an intelligent being endowed with free-will and self-movement": now that we have treated of the exemplar, i.e. God, and of those things which came forth from the power of God in accordance with His will; it remains for us to treat of His image, i.e. man, inasmuch as he too is the principle of his actions, as having free-will and control of his actions.

OF MAN'S LAST END (In Eight Articles)

In this matter we shall consider first the last end of human life; and secondly, those things by means of which man may advance towards this end, or stray from the path: for the end is the rule of whatever is ordained to the end. And since the last end of human life is stated to be happiness, we must consider (1) the last end in general; (2) happiness.

Under the first head there are eight points of inquiry:

(1) Whether it belongs to man to act for an end?

(2) Whether this is proper to the rational nature?

(3) Whether a man's actions are specified by their end?

(4) Whether there is any last end of human life?

(5) Whether one man can have several last ends?

(6) Whether man ordains all to the last end?

(7) Whether all men have the same last end?

(8) Whether all other creatures concur with man in that last end?

FIRST ARTICLE [I-II, Q. 1, Art. 1]

Whether It Belongs to Man to Act for an End?

Objection 1: It would seem that it does not belong to man to act for an end. For a cause is naturally first. But an end, in its very name, implies something that is last. Therefore an end is not a cause. But that for which a man acts, is the cause of his action; since this preposition "for" indicates a relation of causality. Therefore it does not belong to man to act for an end.

Obj. 2: Further, that which is itself the last end is not for an end. But in some cases the last end is an action, as the Philosopher states (Ethic. i, 1). Therefore man does not do everything for an end.

Obj. 3: Further, then does a man seem to act for an end, when he acts deliberately. But man does many things without deliberation, sometimes not even thinking of what he is doing; for instance when one moves one's foot or hand, or scratches one's beard, while intent on something else. Therefore man does not do everything for an end.