y in so far as sin is
itself a diminution of the good of nature, through being an
inordinateness of action. But as regards the inordinateness of the
agent, we must say that such like inordinateness is caused by the
fact that in the acts of the soul, there is an active, and a passive
element: thus the sensible object moves the sensitive appetite, and
the sensitive appetite inclines the reason and will, as stated above
(Q. 77, AA. 1, 2). The result of this is the inordinateness, not as
though an accident acted on its own subject, but in so far as the
object acts on the power, and one power acts on another and puts it
out of order.
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SECOND ARTICLE [I-II, Q. 85, Art. 2]

Whether the Entire Good of Human Nature Can Be Destroyed by Sin?

Objection 1: It would seem that the entire good of human nature can
be destroyed by sin. For the good of human nature is finite, since
human nature itself is finite. Now any finite thing is entirely taken
away, if the subtraction be continuous. Since therefore the good of
nature can be continually diminished by sin, it seems that in the end
it can be entirely taken away.

Obj. 2: Further, in a thing of one nature, the whole and the parts
are uniform, as is evidently the case with air, water, flesh and all
bodies with similar parts. But the good of nature is wholly uniform.
Since therefore a part thereof can be taken away by sin, it seems
that the whole can also be taken away by sin.

Obj. 3: Further, the good of nature, that is weakened by sin, is
aptitude for virtue. Now this aptitude is destroyed entirely in some
on account of sin: thus the lost cannot be restored to virtue any
more than the blind can to sight. Therefore sin can take away the
good of nature entirely.

_On the contrary,_ Augustine says (Enchiridion xiv) that "evil does
not exist except in some good." But the evil of sin cannot be in the
good of virtue or of grace, because they are contrary to it.
Therefore it must be in the good of nature, and consequently it does
not destroy it entirely.

_I answer that,_ As stated above (A. 1), the good of nature, that is
diminished by sin, is the natural inclination to virtue, which is
befitting to man from the very fact that he is a rational being; for
it is due to this that he performs actions in accord with reason,
which is to act virtuously. Now sin cannot entirely take away from
man the fact that he is a rational being, for then he would no longer