Objection 1. It would seem that political prudence is not fittingly accounted a part of prudence. For regnative is a part of political prudence, as stated above (Article 1). But a part should not be reckoned a species with the whole. Therefore political prudence should not be reckoned a part of prudence.
Objection 2. Further, the species of habits are distinguished by their various objects. Now what the ruler has to command is the same as what the subject has to execute. Therefore political prudence as regards the subjects, should not be reckoned a species of prudence distinct from regnative prudence.
Objection 3. Further, each subject is an individual person. Now each individual person can direct himself sufficiently by prudence commonly so called. Therefore there is no need of a special kind of prudence called political.
On the contrary, The Philosopher says (Ethic. vi, 8) that "of the prudence which is concerned with the state one kind is a master-prudence and is called legislative; another kind bears the common name political, and deals with individuals."
I answer that, A slave is moved by his master, and a subject by his ruler, by command, but otherwise than as irrational and inanimate beings are set in motion by their movers. For irrational and inanimate beings are moved only by others and do not put themselves in motion, since they have no free-will whereby to be masters of their own actions, wherefore the rectitude of their government is not in their power but in the power of their movers. On the other hand, men who are slaves or subjects in any sense, are moved by the commands of others in such a way that they move themselves by their free-will; wherefore some kind of rectitude of government is required in them, so that they may direct themselves in obeying their superiors; and to this belongs that species of prudence which is called political.
Reply to Objection 1. As stated above, regnative is the most perfect species of prudence, wherefore the prudence of subjects, which falls short of regnative prudence, retains the common name of political prudence, even as in logic a convertible term which does not denote the essence of a thing retains the name of "proper."
Reply to Objection 2. A different aspect of the object diversifies the species of a habit, as stated above (Question 47, Article 5). Now the same actions are considered by the king, but under a more general aspect, as by his subjects who obey: since many obey one king in various departments. Hence regnative prudence is compared to this political prudence of which we are speaking, as mastercraft to handicraft.
Reply to Objection 3. Man directs himself by prudence commonly so called, in relation to his own good, but by political prudence, of which we speak, he directs himself in relation to the common good.
Source: Summa Theologica (New Advent)