first principles, one good and the
other evil, fell into this error from the same cause, whence also
arose other strange notions of the ancients; namely, because they
failed to consider the universal cause of all being, and considered
only the particular causes of particular effects. For on that account,
if they found a thing hurtful to something by the power of its own
nature, they thought that the very nature of that thing was evil; as,
for instance, if one should say that the nature of fire was evil
because it burnt the house of a poor man. The judgment, however, of
the goodness of anything does not depend upon its order to any
particular thing, but rather upon what it is in itself, and on its
order to the whole universe, wherein every part has its own perfectly
ordered place, as was said above (Q. 47, A. 2, ad 1).

Likewise, because they found two contrary particular causes of two
contrary particular effects, they did not know how to reduce these
contrary particular causes to the universal common cause; and
therefore they extended the contrariety of causes even to the first
principles. But since all contraries agree in something common, it
is necessary to search for one common cause for them above their own
contrary proper causes; as above the contrary qualities of the
elements exists the power of a heavenly body; and above all things
that exist, no matter how, there exists one first principle of being,
as was shown above (Q. 2, A. 3).

Reply Obj. 1: Contraries agree in one genus, and they also agree
in the nature of being; and therefore, although they have contrary
particular causes, nevertheless we must come at last to one first
common cause.

Reply Obj. 2: Privation and habit belong naturally to the same
subject. Now the subject of privation is a being in potentiality, as
was said above (Q. 48, A. 3). Hence, since evil is privation of good,
as appears from what was said above (Q. 48, AA. 1, 2, 3), it is
opposed to that good which has some potentiality, but not to the
supreme good, who is pure act.

Reply Obj. 3: Increase in intensity is in proportion to the nature
of a thing. And as the form is a perfection, so privation removes a
perfection. Hence every form, perfection, and good is intensified by
approach to the perfect term; but privation and evil by receding from
that term. Hence a thing is not said to be evil and worse, by reason
of access to the supreme evil, in the same way as it is said to be
good