Objection 1. It would seem that prudence does not take cognizance of singulars. For prudence is in the reason, as stated above (1 and 2). But "reason deals with universals," according to Phys. i, 5. Therefore prudence does not take cognizance except of universals.
Objection 2. Further, singulars are infinite in number. But the reason cannot comprehend an infinite number of things. Therefore prudence which is right reason, is not about singulars.
Objection 3. Further, particulars are known by the senses. But prudence is not in a sense, for many persons who have keen outward senses are devoid of prudence. Therefore prudence does not take cognizance of singulars.
On the contrary, The Philosopher says (Ethic. vi, 7) that "prudence does not deal with universals only, but needs to take cognizance of singulars also."
I answer that, As stated above (1, ad 3), to prudence belongs not only the consideration of the reason, but also the application to action, which is the end of the practical reason. But no man can conveniently apply one thing to another, unless he knows both the thing to be applied, and the thing to which it has to be applied. Now actions are in singular matters: and so it is necessary for the prudent man to know both the universal principles of reason, and the singulars about which actions are concerned.
Reply to Objection 1. Reason first and chiefly is concerned with universals, and yet it is able to apply universal rules to particular cases: hence the conclusions of syllogisms are not only universal, but also particular, because the intellect by a kind of reflection extends to matter, as stated in De Anima iii.
Reply to Objection 2. It is because the infinite number of singulars cannot be comprehended by human reason, that "our counsels are uncertain" (Wisdom 9:14). Nevertheless experience reduces the infinity of singulars to a certain finite number which occur as a general rule, and the knowledge of these suffices for human prudence.
Reply to Objection 3. As the Philosopher says (Ethic. vi, 8), prudence does not reside in the external senses whereby we know sensible objects, but in the interior sense, which is perfected by memory and experience so as to judge promptly of particular cases. This does not mean however that prudence is in the interior sense as in its principle subject, for it is chiefly in the reason, yet by a kind of application it extends to this sense.
Source: Summa Theologica (New Advent)