Aristotle, Nicomachean Ethics
H. Rackham, Ed.

Art, therefore, as has been said, is a rational quality, concerned with making, that reasons truly. Its opposite, Lack of Art, is a rational quality, concerned with making, that reasons falsely. Both deal with that which admits of variation.5.

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. [2] 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. [3]

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,