3: By prudence man makes precepts not only for others, but
also for himself, as stated above (Q. 47, A. 12, ad 3). Hence as
stated (Ethic. vi, 11), even in subjects, there is place for
prudence; to which docility pertains. And yet even the learned should
be docile in some respects, since no man is altogether
self-sufficient in matters of prudence, as stated above.
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FOURTH ARTICLE [II-II, Q. 49, Art. 4]

Whether Shrewdness Is Part of Prudence?

Objection 1: It would seem that shrewdness is not a part of prudence.
For shrewdness consists in easily finding the middle term for
demonstrations, as stated in _Poster._ i, 34. Now the reasoning of
prudence is not a demonstration since it deals with contingencies.
Therefore shrewdness does not pertain to prudence.

Obj. 2: Further, good counsel pertains to prudence according to
_Ethic._ vi, 5, 7, 9. Now there is no place in good counsel for
shrewdness [*Ethic. vi, 9; Poster. i, 34] which is a kind of
_eustochia_, i.e. "a happy conjecture": for the latter is
"unreasoning and rapid," whereas counsel needs to be slow, as stated
in _Ethic._ vi, 9. Therefore shrewdness should not be accounted a
part of prudence.

Obj. 3: Further, shrewdness as stated above (Q. 48) is a "happy
conjecture." Now it belongs to rhetoricians to make use of
conjectures. Therefore shrewdness belongs to rhetoric rather than to
prudence.

_On the contrary,_ Isidore says (Etym. x): "A solicitous man is one
who is shrewd and alert (_solers citus_)." But solicitude belongs to
prudence, as stated above (Q. 47, A. 9). Therefore shrewdness does
also.

_I answer that,_ Prudence consists in a right estimate about matters
of action. Now a right estimate or opinion is acquired in two ways,
both in practical and in speculative matters, first by discovering it
oneself, secondly by learning it from others. Now just as docility
consists in a man being well disposed to acquire a right opinion from
another man, so shrewdness is an apt disposition to acquire a right
estimate by oneself, yet so that shrewdness be taken for _eustochia_,
of which it is a part. For _eustochia_ is a happy conjecture about
any matter, while shrewdness is "an easy and rapid conjecture in
finding the middle term" (Poster. i, 34). Nevertheless the
philosopher [*Andronicus; Cf. Q. 48, Obj. 1] who calls shrewdness a
part of prudence, takes it for _eustochia_, in general, hence he
says: "Shrewdness is a habit whereby cong