_ We have spoken above (Q. 51, AA. 2, 3) in a general
way about the production of habits from acts; and speaking now in a
special way of this matter in relation to virtue, we must take note
that, as stated above (Q. 55, AA. 3, 4), man's virtue perfects him in
relation to good. Now since the notion of good consists in "mode,
species, and order," as Augustine states (De Nat. Boni. iii) or in
"number, weight, and measure," as expressed in Wis. 11:21, man's good
must needs be appraised with respect to some rule. Now this rule is
twofold, as stated above (Q. 19, AA. 3, 4), viz. human reason and
Divine Law. And since Divine Law is the higher rule, it extends to
more things, so that whatever is ruled by human reason, is ruled by
the Divine Law too; but the converse does not hold.

It follows that human virtue directed to the good which is defined
according to the rule of human reason can be caused by human acts:
inasmuch as such acts proceed from reason, by whose power and rule
the aforesaid good is established. On the other hand, virtue which
directs man to good as defined by the Divine Law, and not by human
reason, cannot be caused by human acts, the principle of which is
reason, but is produced in us by the Divine operation alone. Hence
Augustine in giving the definition of the latter virtue inserts the
words, "which God works in us without us" (Super Ps. 118, Serm.
xxvi). It is also of these virtues that the First Objection holds
good.

Reply Obj. 2: Mortal sin is incompatible with divinely infused
virtue, especially if this be considered in its perfect state. But
actual sin, even mortal, is compatible with humanly acquired virtue;
because the use of a habit in us is subject to our will, as stated
above (Q. 49, A. 3): and one sinful act does not destroy a habit of
acquired virtue, since it is not an act but a habit, that is directly
contrary to a habit. Wherefore, though man cannot avoid mortal sin
without grace, so as never to sin mortally, yet he is not hindered
from acquiring a habit of virtue, whereby he may abstain from evil in
the majority of cases, and chiefly in matters most opposed to reason.
There are also certain mortal sins which man can nowise avoid without
grace, those, namely, which are directly opposed to the theological
virtues, which are in us through the gift of grace. This, however,
will be more fully explained later (Q. 109, A. 4).

Reply Obj. 3: As stated above (A. 1; Q. 51, A. 1), certain seeds or