I answer that, Parts are of three kinds, namely, integral, as wall, roof, and foundations are parts of a house; subjective, as ox and lion are parts of animal; and potential, as the nutritive and sensitive powers are parts of the soul. Accordingly, parts can be assigned to a virtue in three ways. First, in likeness to integral parts, so that the things which need to concur for the perfect act of a virtue, are called the parts of that virtue. In this way, out of all the things mentioned above, eight may be taken as parts of prudence, namely, the six assigned by Macrobius; with the addition of a seventh, viz. memory mentioned by Tully; and eustochia or shrewdness mentioned by Aristotle. For the sense of prudence is also called understanding: wherefore the Philosopher says (Ethic. vi, 11): "Of such things one needs to have the sense, and this is understanding." Of these eight, five belong to prudence as a cognitive virtue, namely, _memory, reasoning, understanding, docility and shrewdness: while the three others belong thereto, as commanding and applying knowledge to action, namely, foresight, circumspection and caution. The reason of their difference is seen from the fact that three things may be observed in reference to knowledge. In the first place, knowledge itself, which, if it be of the past, is called memory, if of the present, whether contingent or necessary, is called understanding or intelligence. Secondly, the acquiring of knowledge, which is caused either by teaching, to which pertains docility, or by discovery, and to this belongs to eustochia, i.e. "a happy conjecture," of which shrewdness is a part, which is a "quick conjecture of the middle term," as stated in Poster. i, 9. Thirdly, the use of knowledge, in as much as we proceed from things known to knowledge or judgment of other things, and this belongs to reasoning. And the reason, in order to command aright, requires to have three conditions. First, to order that which is befitting the end, and this belongs to foresight; secondly, to attend to the circumstances of the matter in hand, and this belongs to circumspection; thirdly, to avoid obstacles, and this belongs to caution.

The subjective parts of a virtue are its various species. In this way the parts of prudence, if we take them properly, are the prudence whereby a man rules himself, and the prudence whereby a man governs a multitude, which differ specifically as stated above (Q. 47, A. 11). Again, the prudence whereby a multitude is governed, is divided into various species according to the various kinds of multitude. There is the multitude which is united together for some particular purpose; thus an army is gathered together to fight, and the prudence that governs this is called military. There is also the multitude that is united together for the whole of life; such is the multitude of a home or family, and this is ruled by domestic prudence: and such again is the multitude of a city or kingdom, the ruling principle of which is regnative prudence in the ruler, and political prudence, simply so called, in the subjects.

If, however, prudence be taken in a wide sense, as including also speculative knowledge, as stated above (Q. 47, A. 2, ad 2) then its parts include dialectics, rhetoric and physics, according to three methods of prudence in the sciences. The first of these is the attaining of science by demonstration, which belongs to physics (if physics be understood to comprise all demonstrative sciences). The second method is to arrive at an opinion through probable premises, and this belongs to dialectics. The third method is to employ conjectures in order to induce a certain suspicion, or to persuade somewhat, and this belongs to rhetoric. It may be said, however, that these three belong also to prudence properly so called, since it argues sometimes from necessary premises, sometimes from probabilities, and sometimes from conjectures.

The potential parts of a virtue are the virtues connected with it, which are directed to certain secondary acts or matters, not having, as it were, the whole power of the principal virtue. In this way the parts of prudence are good counsel, which concerns counsel, synesis, which concerns judgment in matters of ordinary occurrence, and gnome, which concerns judgment in matters of exception to the law: while prudence is about the chief act, viz. that of commanding.