We may arrive at a definition of Prudence by considering who are the persons whom we call
prudent. Now it is held to be the mark of a prudent man to be able to deliberate well
about what is good and advantageous for himself, not in some one department, for instance
what is good for his health or strength, but what is advantageous as a means to the good
life in general.
This is proved by the fact that we also
speak of people as prudent or wise in some particular thing, when they calculate well with
a view to attaining some particular end of value （other than those ends which are
the object of an art）; so that the prudent man in general will be the man who is
good at deliberating in general.
But no one deliberates about things that cannot vary, nor about things not within his
power to do. Hence inasmuch as scientific knowledge involves demonstration, whereas things
whose fundamental principles are variable are not capable of demonstration, because
everything about them is variable, and inasmuch as one cannot deliberate about things that are of
necessity, it follows that Prudence is not the same as Science. Nor can it be the same as
Art. It is not Science, because matters of conduct admit of variation; and not Art,
because doing and making are generically different,1
since making aims at an end distinct from
the act of making, whereas in doing the end cannot be other than the act itself: doing
is in itself the end.
It remains therefore that it is a truth-attaining
rational quality, concerned with action in relation to things that are good and bad for
Hence men like Pericles are deemed prudent, because they possess a faculty of discerning
what things are good for themselves and for mankind and that is our conception of an
expert in Domestic Economy or Political Science.
（This also accounts for the word Temperance,3
which signifies ‘preserving prudence.’
And Temperance does in fact preserve our belief as to our own good; for pleasure and
pain do not destroy or pervert all beliefs, for instance, the belief that the three angles
of a triangle are, or are not, together equal to two right angles, but only beliefs
concerning action. The first principles of action are the end to which our acts are means;
but a man corrupted by a love of pleasure or fear of pain, entirely fails to discern any
and cannot see that he ought to choose and do everything as a means
to this end, and for its sake; for vice tends to destroy the sense of principle.5
It therefore follows that Prudence is a truth-attaining rational quality, concerned with
action in relation to the things that are good for human beings.
Moreover, we can speak of excellence in Art,6
but not of excellence in Prudence. Also in Art
voluntary error is not so bad as involuntary, whereas in the sphere of Prudence it is
worse, as it is in the sphere of the virtues. It is therefore clear that Prudence is an
excellence or virtue, and not an Art.
Of the two parts of the soul possessed of reason, Prudence must be the virtue of one,
namely, the part that forms opinions7
; for Opinion deals with that which can vary, and so does
Prudence. But yet Prudence is not a rational quality merely, as shown by the fact that a
purely rational faculty can be forgotten, whereas a failure in Prudence is not a mere
lapse of memory.8