1628. The Objects of the Act of Prudence.—(a) Prudence is concerned, not with speculative truth (i.e., with those things that are known for the sake of knowledge), but with practical truth (i.e., with those things that are known for the sake of use). It aims, not to investigate and discover what is the nature of virtue, but to guide man so that he may become virtuous and practise virtue. It should be noted, however, that the acts of the speculative reason, although they do not belong to prudence itself, are like other acts subject to the direction of prudence; for in pursuing speculative studies one should use good judgment as to the subjects to be considered, the time, place, manner, etc., of study.
(b) Prudence is not concerned with necessary truths and first principles of morality, but with their application to contingent and particular cases, just as a physician is called on to cure, not a universal or abstract man, but the particular and individual man before him. But since one cannot well apply that of which one is ignorant, the prudent man must be acquainted both with the general rules of right living and with the particular things to which his knowledge is to be applied. He lacks prudence, therefore, who from vincible ignorance does not know a general principle (e.g., that too much drink is bad), or a case to which that principle should be applied (e.g., that the quantity of drink before one is too much).
1629. It is customary to distinguish a twofold object of a virtue, namely, the material object (i.e., the kind of activity the virtue perfects, whether in the field of knowledge, or of action, or of production) and the formal object (i.e., the special viewpoint of goodness from which the material object is considered).
(a) The material object of prudence embraces individual human actions performed under choice and freely (_agibilia_). (b) The formal object of prudence is the right deliberation, decision, and direction (_recta ratio_) to be given to human actions, with a view to the observance of the golden mean.
1630. Necessity of Certitude.—Prudence, being an intellectual virtue, must have certainty (see on the Certain Conscience, 640 sqq.). But with regard to particular contingencies (e.g., whether Balbus ought to marry Caia) there are various kinds of certainty.
(a) There is the certainty of knowledge based on a generalization from experience of what happens in the majority of cases (e.g., that persons well mated by reason of birth, age, dispositions, etc., marry successfully). This kind of certainty belongs to moral science.
(b) There is also a certainty of knowledge based on the indications in a particular case (e.g., that Balbus and Caia appear to have congenial dispositions and a mutual affection that will make their marriage a success). This is the certainty of opinion, and while it may suffice as a rule for conscience (see the Systems of Conscience, 672 sqq.), events do not always verify its predictions. Hence it is said: “The thoughts of mortal men are fearful and our counsels uncertain” (Wis., ix. 14).
(c) There is finally the certainty of practical truth, which consists in harmony with a good will. This is the certainty that is proper to prudence, for this virtue is not a matter of reason alone. Hence, even though a matter properly decided on should not take place or should fail of the purpose intended (e.g., if the marriage of Balbus and Caia is prevented or turns out badly), it remains that prudence was not deceived in its decision, for that decision when made was according to right reason and a good will (see 578).
1631. Relation of Prudence to the Other Moral Virtues.—(a) Prudence does not direct the moral virtues to their own proper ends; for the knowledge of those ends comes from synteresis, or moral understanding (i.e., the natural perception of the first principles of right and wrong), while the inclination to those ends is from the moral virtues themselves. Prudence does not deal with first principles, nor is it an inclination towards particular ends. Hence, it is the intellectual virtue of synteresis that directs the moral virtues through the dictate that right reason must be followed, that moderation must be observed, that the passions of anger, pleasure, sorrow, etc., must be so regulated that both extremes of excess and defect will be avoided.
(b) Prudence directs the moral virtues to the ways and means by which their ends are to be attained; for the regulation of things particular and variable, such as ways and means, pertains to prudence. Synteresis is concerned with necessary principles, and the moral virtues give a uniform and steady inclination to follow the mean of right reason, but neither the one nor the other can indicate how principles are to be applied or how inclinations are to be put in practice. Hence, it is the work of moral science to determine what or how much anger, pleasure, sorrow, etc., is moderate for the average case; but prudence has to decide this for a particular case here and now (see on Conscience, 575). Without prudence bravery becomes foolhardiness, temperance degenerates into fanaticism, and mercy changes to weakness.