Does man act for the sake of an end? The Objectors claim not; Aquinas disagrees.
Aquinas argues that things within the same genus[*] share a common principle. And since, as Aristotle writes, the end is the principle in human operations (Phys. ii, 9), therefore man acts for an end. Here is an expanded picture of the syllogism[*]:
Major: All things contained in a genus share the same common principle.
Minor: The end is the principle in human operations.
Conclusion: All human operations are ordered to an end.
He then distinguishes two types of actions. One is when a man uses his faculty of reason and deliberate will to act, which he classifies as a human action. The other is non-deliberate acts, which are acts of a man, not properly human, and will be relevant to Reply Obj. 3.
He proceeds:
Whatever actions proceed from a power, are caused by that power in accordance with the nature of the object. But the object of the will is the end and the good. Therefore all human actions must be for an end.
Syllogism:
Major: Whatever actions proceed from a power are caused by that power in accordance with the nature of the object.
Minor: The object of the will is the end and the good.
Conclusion: All human actions must be for an end.
Object -> Power -> Action
1. Object: The good and the end as known by the intellect.
2. Power: The will.
3. Action: The chosen action.
Objector 1:
It would seem that it does not belong to man to act for an end. For a cause is naturally first. But for 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.
Reply Objection 1:
The end may be last in order, though the man's intentions are derived from the end. In this way, the intentions for the end are the cause.
Objector 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.
Syllogism:
Major: That which is itself the last end is not for an end.
Minor: Sometimes, the last end is an action.
Conclusion: Man does not do everything for an end.
Reply Objection 2:
If a human action is the last end[*], then it must be voluntary. There are two kinds of voluntary actions. First, because it is commanded by the will (ex: to walk, or to speak). Second, because the will elicits it (ex: the very act of willing). The very act of willing cannot be the last end. The object of the will is the end. Connect the example below to the "Object -> Power -> Action" demonstration above.
An example of a last end is contemplation. The will elicits the act of contemplation (and may command external acts ordered to it), through which the object is the good and truth contemplated.
Thus, the end cannot be the very act of willing. Consequently, if a human action is the last end, it must be commanded by the will. Therefore, every human act, including acts called ‘ends’, is ordered to the good as its end. Even when an operation is called the end, it is so because it attains or contains its object (the good).
Objector 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.
Syllogism:
Major: Man seems to act for an end when he acts deliberately.
Minor: Man does many things without deliberation.
Conclusion: Man does not do everything for an end.
Reply Objection 3:
Such like actions are not properly human actions; since they do not proceed from deliberation of the reason, which is the proper principle of human actions. Therefore they have indeed an imaginary end, but not one that is fixed by reason.
What he means by imaginary end is an end that appears good in the head, while it may or may not correspond to reality, an apparent good. For example, someone pursues a false end (ex: thinks pleasure = highest good); he is still acting for an end, but a misjudged one.