Objection 1. It would seem that prudence is not in the cognitive but in the appetitive faculty. For Augustine says (De Morib. Eccl. xv): "Prudence is love choosing wisely between the things that help and those that hinder." Now love is not in the cognitive, but in the appetitive faculty. Therefore prudence is in the appetitive faculty.
Objection 2. Further, as appears from the foregoing definition it belongs to prudence "to choose wisely." But choice is an act of the appetitive faculty, as stated above (I-II, 13, 1). Therefore prudence is not in the cognitive but in the appetitive faculty.
Objection 3. Further, the Philosopher says (Ethic. vi, 5) that "in art it is better to err voluntarily than involuntarily, whereas in the case of prudence, as of the virtues, it is worse." Now the moral virtues, of which he is treating there, are in the appetitive faculty, whereas art is in the reason. Therefore prudence is in the appetitive rather than in the rational faculty.
On the contrary, Augustine says (QQ. lxxxiii, qu. 61): "Prudence is the knowledge of what to seek and what to avoid."
I answer that, As Isidore says (Etym. x): "A prudent man is one who sees as it were from afar, for his sight is keen, and he foresees the event of uncertainties." Now sight belongs not to the appetitive but to the cognitive faculty. Wherefore it is manifest that prudence belongs directly to the cognitive, and not to the sensitive faculty, because by the latter we know nothing but what is within reach and offers itself to the senses: while to obtain knowledge of the future from knowledge of the present or past, which pertains to prudence, belongs properly to the reason, because this is done by a process of comparison. It follows therefore that prudence, properly speaking, is in the reason.
Reply to Objection 1. As stated above (I, 82, 4) the will moves all the faculties to their acts. Now the first act of the appetitive faculty is love, as stated above (I-II, 25, 1 and 2). Accordingly prudence is said to be love, not indeed essentially, but in so far as love moves to the act of prudence. Wherefore Augustine goes on to say that "prudence is love discerning aright that which helps from that which hinders us in tending to God." Now love is said to discern because it moves the reason to discern.
Reply to Objection 2. The prudent man considers things afar off, in so far as they tend to be a help or a hindrance to that which has to be done at the present time. Hence it is clear that those things which prudence considers stand in relation to this other, as in relation to the end. Now of those things that are directed to the end there is counsel in the reason, and choice in the appetite, of which two, counsel belongs more properly to prudence, since the Philosopher states (Ethic. vi, 5,7,9) that a prudent man "takes good counsel." But as choice presupposes counsel, since it is "the desire for what has been already counselled" (Ethic. iii, 2), it follows that choice can also be ascribed to prudence indirectly, in so far, to wit, as prudence directs the choice by means of counsel.
Reply to Objection 3. The worth of prudence consists not in thought merely, but in its application to action, which is the end of the practical reason. Wherefore if any defect occur in this, it is most contrary to prudence, since, the end being of most import in everything, it follows that a defect which touches the end is the worst of all. Hence the Philosopher goes on to say (Ethic. vi, 5) that prudence is "something more than a merely rational habit," such as art is, since, as stated above (I-II, 57, 4) it includes application to action, which application is an act of the will.
Source: Summa Theologica (New Advent)