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