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 {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.
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 {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] who calls shrewdness a part of prudence, takes it for {eustochia}, 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 {euboulia}, i.e. good counsel, is not {eustochia}, 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.
II–II · Q. 49, Art. 5: Whether reason should be reckoned a part of prudence?
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
Objection 3: Further, reason as a power does not differ essentially from the intelligence, as stated above (FP, Q 79, A 8). If therefore intelligence be reckoned a part of prudence, it is superfluous to add reason.
On the contrary, Macrobius [*In Somn. Scip. i], following the opinion of Plotinus, numbers reason among the parts of prudence.
I answer that, The work of prudence is to take good counsel, as stated in Ethic. vi, 7. Now counsel is a research proceeding from certain things to others. But this is the work of reason. Wherefore it is requisite for prudence that man should be an apt reasoner. And since the things required for the perfection of prudence are called requisite or quasi-integral parts of prudence, it follows that reason should be numbered among these parts.
Reply to Objection 1: Reason denotes here, not the power of reason, but its good use.
Reply to Objection 2: The certitude of reason comes from the intellect. Yet the need of reason is from a defect in the intellect, since those things in which the intellective power is in full vigor, have no need for reason, for they comprehend the truth by their simple insight, as do God and the angels. On the other hand particular matters of action, wherein prudence guides, are very far from the condition of things intelligible, and so much the farther, as they are less certain and fixed. Thus matters of art, though they are singular, are nevertheless more fixed and certain, wherefore in many of them there is no room for counsel on account of their certitude, as stated in Ethic. iii, 3. Hence, although in certain other intellectual virtues reason is more certain than in prudence, yet prudence above all requires that man be an apt reasoner, so that he may rightly apply universals to particulars, which latter are various and uncertain.
Reply to Objection 3: Although intelligence and reason are not different powers, yet they are named after different acts. For intelligence takes its name from being an intimate penetration of the truth [*Cf. SS, Q 8, A 1], while reason is so called from being inquisitive and discursive. Hence each is accounted a part of reason as explained above (A 2; Q 47, A 2 ,3).