The three parts of philosophy

The first and most necessary division in philosophy is that which has to do with the application of the principles, as, for example, Do not lie. The second deals with the demonstrations, as, for example. How comes it that we ought not to lie? The third confirms and discriminates between these processes, as, for example, How does it come that this is a proof? For what is a proof, what is logical consequence, what contradiction, what truth, what falsehood? Therefore, the third division is necessary because of the second, and the second because of the first; while the most necessary of all, and the one in which we ought to rest, is the first. But we do the opposite; for we spend our time in the third division, and all our zeal is devoted to it, while we utterly neglect the first. Wherefore, we lie, indeed, but are ready with the arguments which prove that one ought not to lie.