I answer that, Understanding denotes here, not the intellectual power, but the right estimate about some final principle, which is taken as self-evident: thus we are said to understand the first principles of demonstrations. Now every deduction of reason proceeds from certain statements which are taken as primary: wherefore every process of reasoning must needs proceed from some understanding. Therefore since prudence is right reason applied to action, the whole process of prudence must needs have its source in understanding. Hence it is that understanding is reckoned a part of prudence.
Reply to Objection 1: The reasoning of prudence terminates, as in a conclusion, in the particular matter of action, to which, as stated above (Q[47], AA[3],6), it applies the knowledge of some universal principle. Now a singular conclusion is argued from a universal and a singular proposition. Wherefore the reasoning of prudence must proceed from a twofold understanding. The one is cognizant of universals, and this belongs to the understanding which is an intellectual virtue, whereby we know naturally not only speculative principles, but also practical universal principles, such as "One should do evil to no man," as shown above (Q[47], A[6]). The other understanding, as stated in Ethic. vi, 11, is cognizant of an extreme, i.e. of some primary singular and contingent practical matter, viz. the minor premiss, which must needs be singular in the syllogism of prudence, as stated above (Q[47], AA[3],6). Now this primary singular is some singular end, as stated in the same place. Wherefore the understanding which is a part of prudence is a right estimate of some particular end.
Reply to Objection 2: The understanding which is a gift of the Holy Ghost, is a quick insight into divine things, as shown above (Q[8], AA[1],2). It is in another sense that it is accounted a part of prudence, as stated above.
Reply to Objection 3: The right estimate about a particular end is called both "understanding," in so far as its object is a principle, and "sense," in so far as its object is a particular. This is what the Philosopher means when he says (Ethic. v, 11): "Of such things we need to have the sense, and this is understanding." But this is to be understood as referring, not to the particular sense whereby we know proper sensibles, but to the interior sense, whereby we judge of a particular.
Whether docility should be accounted a part of prudence?
Objection 1: It would seem that docility should not be accounted a part of prudence. For that which is a necessary condition of every intellectual virtue, should not be appropriated to one of them. But docility is requisite for every intellectual virtue. Therefore it should not be accounted a part of prudence.
Objection 2: Further, that which pertains to a human virtue is in our power, since it is for things that are in our power that we are praised or blamed. Now it is not in our power to be docile, for this is befitting to some through their natural disposition. Therefore it is not a part of prudence.
Objection 3: Further, docility is in the disciple: whereas prudence, since it makes precepts, seems rather to belong to teachers, who are also called "preceptors." Therefore docility is not a part of prudence.
On the contrary, Macrobius [*In Somn. Scip. i, 8] following the opinion of Plotinus places docility among the parts of prudence.
I answer that, As stated above (A[2], ad 1; Q[47], A[3]) prudence is concerned with particular matters of action, and since such matters are of infinite variety, no one man can consider them all sufficiently; nor can this be done quickly, for it requires length of time. Hence in matters of prudence man stands in very great need of being taught by others, especially by old folk who have acquired a sane understanding of the ends in practical matters. Wherefore the Philosopher says (Ethic. vi, 11): "It is right to pay no less attention to the undemonstrated assertions and opinions of such persons as are experienced, older than we are, and prudent, than to their demonstrations, for their experience gives them an insight into principles." Thus it is written ( Prov. 3:5 ): "Lean not on thy own prudence," and ( Ecclus. 6:35 ): "Stand in the multitude of the ancients" (i.e. the old men), "that are wise, and join thyself from thy heart to their wisdom." Now it is a mark of docility to be ready to be taught: and consequently docility is fittingly reckoned a part of prudence
Reply to Objection 1: Although docility is useful for every intellectual virtue, yet it belongs to prudence chiefly, for the reason given above.
Reply to Objection 2: Man has a natural aptitude for docility even as for other things connected with prudence. Yet his own efforts count for much towards the attainment of perfect docility: and he must carefully, frequently and reverently apply his mind to the teachings of the learned, neither neglecting them through laziness, nor despising them through pride.
Reply to Objection 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.
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.
Objection 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 , 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.
Objection 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 , of which it is a part. For 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 , in general, hence he says: "Shrewdness is a habit whereby congruities are discovered rapidly."
Reply to Objection 1: Shrewdness is concerned with the discovery of the middle term not only in demonstrative, but also in practical syllogisms, as, for instance, when two men are seen to be friends they are reckoned to be enemies of a third one, as the Philosopher says (Poster. i, 34). In this way shrewdness belongs to prudence.
Reply to Objection 2: The Philosopher adduces the true reason (Ethic. vi, 9) to prove that , i.e. good counsel, is not , which is commended for grasping quickly what should be done. Now a man may take good counsel, though he be long and slow in so doing, and yet this does not discount the utility of a happy conjecture in taking good counsel: indeed it is sometimes a necessity, when, for instance, something has to be done without warning. It is for this reason that shrewdness is fittingly reckoned a part of prudence.
Reply to Objection 3: Rhetoric also reasons about practical matters, wherefore nothing hinders the same thing belonging both to rhetoric and prudence. Nevertheless, conjecture is taken here not only in the sense in which it is employed by rhetoricians, but also as applicable to all matters whatsoever wherein man is said to conjecture the truth.
Whether reason should be reckoned a part of prudence?
Objection 1: It would seem that reason should not be reckoned a part of prudence. For the subject of an accident is not a part thereof. But prudence is in the reason as its subject (Ethic. vi, 5). Therefore reason should not be reckoned a part of prudence.
Objection 2: Further, that which is common to many, should not be reckoned a part of any one of them; or if it be so reckoned, it should be reckoned a part of that one to which it chiefly belongs. Now reason is necessary in all the intellectual virtues, and chiefly in wisdom and science, which employ a demonstrative reason. Therefore reason should not be reckoned a part of prudence