The first and most necessary point in philosophy is the practice of the maxims, for example, not to lie. The second is the proof of the maxims, as, Whence it comes that one ought not to lie. The third is that which gives confirmation and coherence to these, as, Whence it comes that this is a proof, for what is proof? what is consequence? what is contradiction? what is truth? what is falsehood?
Thus the third point is necessary through the second, and the second through the first. But the most necessary of all, and that where we must rest, is the first. But we do the contrary. For we delay in the third point, and spend all our zeal upon that, while of the first we are utterly careless: we are liars, while we are ready in explaining how it is shown that it is wrong to lie.