t reside in the external senses whereby we know sensible objects,
but in the interior sense, which is perfected by memory and
experience so as to judge promptly of particular cases. This does not
mean however that prudence is in the interior sense as in its
princip[al] subject, for it is chiefly in the reason, yet by a kind
of application it extends to this sense.
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FOURTH ARTICLE [II-II, Q. 47, Art. 4]

Whether Prudence Is a Virtue?

Objection 1: It would seem that prudence is not a virtue. For
Augustine says (De Lib. Arb. i, 13) that "prudence is the science of
what to desire and what to avoid." Now science is condivided with
virtue, as appears in the _Predicaments_ (vi). Therefore prudence is
not a virtue.

Obj. 2: Further, there is no virtue of a virtue: but "there is a
virtue of art," as the Philosopher states (Ethic. vi, 5): wherefore
art is not a virtue. Now there is prudence in art, for it is written
(2 Paralip. ii, 14) concerning Hiram, that he knew "to grave all sort
of graving, and to devise ingeniously (_prudenter_) all that there
may be need of in the work." Therefore prudence is not a virtue.

Obj. 3: Further, no virtue can be immoderate. But prudence is
immoderate, else it would be useless to say (Prov. 23:4): "Set bounds
to thy prudence." Therefore prudence is not a virtue.

_On the contrary,_ Gregory states (Moral. ii, 49) that prudence,
temperance, fortitude and justice are four virtues.

_I answer that,_ As stated above (I-II, Q. 55, A. 3; Q. 56, A. 1)
when we were treating of virtues in general, "virtue is that which
makes its possessor good, and his work good likewise." Now good may
be understood in a twofold sense: first, materially, for the thing
that is good, secondly, formally, under the aspect of good. Good,
under the aspect of good, is the object of the appetitive power.
Hence if any habits rectify the consideration of reason, without
regarding the rectitude of the appetite, they have less of the nature
of a virtue since they direct man to good materially, that is to say,
to the thing which is good, but without considering it under the
aspect of good. On the other hand those virtues which regard the
rectitude of the appetite, have more of the nature of virtue, because
they consider the good not only materially, but also formally, in
other words, they consider that which is good under the aspect of
good.

Now it belongs to prudence, as stated above (A. 1, ad 3;