The virtue of prudence is discussed a lot these days so I thought it would be good to post this section from Fr. Garrigou-Lagrange's work on this virtue. http://www.thesumma.info/reality/reality52.php
REALITY—A Synthesis Of Thomistic Thought
by Reginald Garrigou-Lagrange, O. P.
CH51: THE MORAL VIRTUES
Article One: Prudence
The charioteer among the virtues, the name given to prudence by the ancients, shows that prudence is an intellectual virtue which guides the moral virtues. St. Thomas, following Aristotle, says that prudence is right reason as directing human acts.  This definition is found, proportionally, in acquired prudence which educates and disciplines the will and the sense faculties, and in infused prudence which pours divine light into these faculties. .
Prudence, acquired or infused, determines the golden middle way between extremes, between cowardice, say, and temerity, in the virtue of fortitude. But the medium way of acquired prudence is subordinated to that of infused prudence; as, for example, in the musician finger dexterity is subordinated to the art of music which is in the practical intellect.
Prudence has three acts: first counsel, which scrutinizes the means proposed for an end; second, practical judgment, which immediately directs choice; third, imperium, which directs execution. .
In determining the relation between prudence and the moral virtues, St. Thomas is guided by Aristotle's principle: "As are a man's dispositions, so are his judgments."  If we are ambitious, that is good which flatters our pride. If we are humble, that is good which agrees with humility. No one, then, can give prudent judgments unless he is disposed thereto by justice, temperance, fortitude, loyalty, and modesty, just as, to illustrate, the coachman cannot guide the vehicle well unless he has well-trained horses. This is what St. Thomas means when he says that the truth of the judgment passed by prudence depends on its conformity to well-trained appetites, rational and sensitive. .
Here, as always, we see St. Thomas passing progressively from the common sense of natural reason to philosophic reasoning, all in the service of theology. Thus, even when the judgment of prudence is speculatively false, in consequence of ignorance, say, or of involuntary terror, that judgment is still true in the practical order. To illustrate. When we simply cannot know nor even suspect that the drink offered to us is poisoned, our act of drinking is not imprudent. In the speculative objective order our judgment is not true, but in the practical order it is true, because conformed to right disposition and intention.
This virtuous disposition and intention, necessary for counsel, is more necessary for the imperium. Prudence cannot command unless the will and the sense appetites are seasoned in obedience. Here lies what is called the interconnection of virtues, the union of all virtues in one spiritual organism. Prudence, acquired and infused, is the charioteer whose first task is continual training of his steeds. For the education and formation of a good conscience, the doctrines just explained are excellent guides, more sure, profound, and useful than the shifting balance of conflicting probabilities.
The gift which corresponds to prudence is that of counsel, which gives us divine inspirations in eases where even infused prudence hesitates, in answering, for instance, an indiscreet question, so as neither to lie nor to betray a secret. .