Objection 1. It would seem that prudence can be lost through forgetfulness. For since science is about necessary things, it is more certain than prudence which is about contingent matters of action. But science is lost by forgetfulness. Much more therefore is prudence.
Objection 2. Further, as the Philosopher says (Ethic. ii, 3) "the same things, but by a contrary process, engender and corrupt virtue." Now the engendering of prudence requires experience which is made up "of many memories," as he states at the beginning of his Metaphysics (i, 1). Therefore since forgetfulness is contrary to memory, it seems that prudence can be lost through forgetfulness.
Objection 3. Further, there is no prudence without knowledge of universals.
But knowledge of universals can be lost through forgetfulness. Therefore prudence can also.
On the contrary, The Philosopher says (Ethic. vi, 5) that "forgetfulness is possible to art but not to prudence."
I answer that, Forgetfulness regards knowledge only, wherefore one can forget art and science, so as to lose them altogether, because they belong to the reason. But prudence consists not in knowledge alone, but also in an act of the appetite, because as stated above (Article 8), its principal act is one of command, whereby a man applies the knowledge he has, to the purpose of appetition and operation. Hence prudence is not taken away directly by forgetfulness, but rather is corrupted by the passions. For the Philosopher says (Ethic. vi, 5) that "pleasure and sorrow pervert the estimate of prudence": wherefore it is written (Daniel 13:56): "Beauty hath deceived thee, and lust hath subverted thy heart," and (Exodus 23:8): "Neither shalt thou take bribes which blind even the prudent [Douay: 'wise']."
Nevertheless forgetfulness may hinder prudence, in so far as the latter's command depends on knowledge which may be forgotten.
Reply to Objection 1. Science is in the reason only: hence the comparison fails, as stated above [Cf. I-II, 53, 1].
Reply to Objection 2. The experience required by prudence results not from memory alone, but also from the practice of commanding aright.
Reply to Objection 3. Prudence consists chiefly, not in the knowledge of universals, but in applying them to action, as stated above (Article 3). Wherefore forgetting the knowledge of universals does not destroy the principal part of prudence, but hinders it somewhat, as stated above.
Source: Summa Theologica (New Advent)