The first and most necessary place (part, [Greek: topos]) in philosophy
is the use of theorems (precepts, [Greek: theoraemata]), for instance,
that we must not lie; the second part is that of demonstrations, for
instance, How is it proved that we ought not to lie? The third is that
which is confirmatory of these two, and explanatory, for example, How
is this a demonstration? For what is demonstration, what is
consequence, what is contradiction, what is truth, what is falsehood?
The third part (topic) is necessary on account of the second, and the
second on account of the first; but the most necessary and that on
which we ought to rest is the first. But we do the contrary. For we
spend our time on the third topic, and all our earnestness is about it;
but we entirely neglect the first. Therefore we lie; but the
demonstration that we ought not to lie we have ready to hand.