(CG 3/2). That every Agent acts to some End (Book 3. God, the End of Creatures) (Summa Contra Gentiles) (Aquinas, Thomas, St.)

That to which an agent definitely tends must be suited to it: for it would not tend to the thing except for some suitability to itself. But what is suitable to a thing is good for it. Therefore every agent acts to some good.

6. An intellectual agent acts for an end by determining its own end. A physical agent, though acting for an end, does not determine its own end, having no idea of an end, but moves in the direction of an end determined for it by another. Now an intellectual agent does not fix for itself an end except under some aspect of good: for a term of intellect is a motive only under an aspect of good, which is the object of will. Therefore a physical agent also does not move or act to any end except inasmuch as it is good. Such an agent has its end determined by some natural appetite or tendency.

7. It is part of the same plan of action to shun evil and to seek good. But all things are found to shun evil. Intellectual agents shun a thing for this reason, that they apprehend its evil: while all physical agents, to the full extent of the power that is in them, resist destruction, because that is the evil of everything. All things therefore act to some good.