od. Wherefore in those matters where the prompting of reason is not
sufficient, and there is need for the prompting of the Holy Ghost,
there is, in consequence, need for a gift.

Now man's reason is perfected by God in two ways: first, with its
natural perfection, to wit, the natural light of reason; secondly,
with a supernatural perfection, to wit, the theological virtues, as
stated above (Q. 62, A. 1). And, though this latter perfection is
greater than the former, yet the former is possessed by man in a more
perfect manner than the latter: because man has the former in his
full possession, whereas he possesses the latter imperfectly, since
we love and know God imperfectly. Now it is evident that anything
that has a nature or a form or a virtue perfectly, can of itself work
according to them: not, however, excluding the operation of God, Who
works inwardly in every nature and in every will. On the other hand,
that which has a nature, or form, or virtue imperfectly, cannot of
itself work, unless it be moved by another. Thus the sun which
possesses light perfectly, can shine by itself; whereas the moon
which has the nature of light imperfectly, sheds only a borrowed
light. Again, a physician, who knows the medical art perfectly, can
work by himself; but his pupil, who is not yet fully instructed,
cannot work by himself, but needs to receive instructions from him.

Accordingly, in matters subject to human reason, and directed to
man's connatural end, man can work through the judgment of his
reason. If, however, even in these things man receive help in the
shape of special promptings from God, this will be out of God's
superabundant goodness: hence, according to the philosophers, not
every one that had the acquired moral virtues, had also the heroic or
divine virtues. But in matters directed to the supernatural end, to
which man's reason moves him, according as it is, in a manner, and
imperfectly, informed by the theological virtues, the motion of
reason does not suffice, unless it receive in addition the prompting
or motion of the Holy Ghost, according to Rom. 8:14, 17: "Whosoever
are led by the Spirit of God, they are sons of God . . . and if sons,
heirs also": and Ps. 142:10: "Thy good Spirit shall lead me into the
right land," because, to wit, none can receive the inheritance of
that land of the Blessed, except he be moved and led thither by the
Holy Ghost. Therefore, in order to accomplish this end, it is
necessary