It will also turn out that there are other starting points for demonstrations, after the source which takes its rise in faith,—the things which appear clearly to sensation and understanding. For the phenomena of sensation are simple, and incapable of being decompounded; but those of understanding are simple, rational, and primary. But those produced from them are compound, but no less clear and reliable, and having more to do with the reasoning faculty than the first. For therefore the peculiar native power of reason, which we all have by nature, deals with agreement and disagreement. If, then, any argument be found to be of such a kind, as from points already believed to be capable of producing belief in what is not yet believed, we shall aver that this is the very essence of demonstration.