Book 6: The Intellectual Virtues.
That which is variable includes that which man makes and that which man does; but making or production is different from doing or action (here we adopt the popular distinctions). The habit or formed faculty of acting with reason or calculation, then, is different from the formed faculty of producing with reason or calculation. And so the one cannot include the other; for action is not production, nor is production action.
Now, the builder’s faculty is one of the arts, and may be described as a certain formed faculty of producing with calculation; and there is no art which is not a faculty of this kind, nor is there any faculty of this kind which is not an art: an art, then, is the same thing as a formed faculty of producing with correct calculation.
And every art is concerned with bringing something into being, i.e. with contriving or calculating how to bring into being some one of those things that can either be or not be, and the cause of whose production lies in the producer, not in the thing itself which is produced. For art has not to do with that which is or comes into being of necessity, nor with the products of nature; for these have the cause of their production in themselves.
Production and action being different, art of course has to do with production, and not with action. And, in a certain sense, its domain is the same as that of chance or fortune, as Agathon says—
“Art waits on fortune, fortune waits on art.”
Art, then, as we said, is a certain formed faculty or habit of production with correct reasoning or calculation, and the contrary of this (ἀτεχνία) is a habit of production with incorrect calculation, the field of both being that which is variable.