Reply Obj. 2:  If any human action be the last end, it must be voluntary, else it would not be human, as stated above.  Now an action is voluntary in one of two ways:  first, because it is commanded by the will, e.g. to walk, or to speak; secondly, because it is elicited by the will, for instance the very act of willing.  Now it is impossible for the very act elicited by the will to be the last end.  For the object of the will is the end, just as the object of sight is color:  wherefore just as the first visible cannot be the act of seeing, because every act of seeing is directed to a visible object; so the first appetible, i.e. the end, cannot be the very act of willing.  Consequently it follows that if a human action be the last end, it must be an action commanded by the will:  so that there, some action of man, at least the act of willing, is for the end.  Therefore whatever a man does, it is true to say that man acts for an end, even when he does that action in which the last end consists.

Reply Obj. 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. ________________________

Second article [I-ii, Q. 1, Art. 2]

Whether It Is Proper to the Rational Nature to Act for an End?

Objection 1:  It would seem that it is proper to the rational nature to act for an end.  For man, to whom it belongs to act for an end, never acts for an unknown end.  On the other hand, there are many things that have no knowledge of an end; either because they are altogether without knowledge, as insensible creatures:  or because they do not apprehend the idea of an end as such, as irrational animals.  Therefore it seems proper to the rational nature to act for an end.

Obj. 2:  Further, to act for an end is to order one’s action to an end.  But this is the work of reason.  Therefore it does not belong to things that lack reason.

Obj. 3:  Further, the good and the end is the object of the will.  But “the will is in the reason” (De Anima iii, 9).  Therefore to act for an end belongs to none but a rational nature.

On the contrary, The Philosopher proves (Phys. ii, 5) that “not only mind but also nature acts for an end.”

I answer that, Every agent, of necessity, acts for an end.  For if, in a number of causes ordained to one another, the first be removed, the others must, of necessity, be removed also.  Now the first of all causes is the final cause.  The reason of which is that matter does not receive form, save in so far as it is moved by an agent; for nothing reduces itself from potentiality to act.  But an agent does not move except out of intention for an end.  For if the agent were not determinate to some particular effect, it would not do one thing rather than another:  consequently in order that it produce a determinate effect, it must, of necessity, be determined to some certain one, which has the nature of an end.  And just as this determination is effected, in the rational nature, by the “rational appetite,” which is called the will; so, in other things, it is caused by their natural inclination, which is called the “natural appetite.”