in common, which is discourse (λόγος), establishing one thing from others. But the grounds from which the point in question is to be established, must be admitted and known by the learner. And the foundation of all these is what is evident to sense and to intellect.
Accordingly the primary demonstration is composed of all these. But the demonstration which, from points already demonstrated thereby, concludes some other point, is no less reliable than the former. It cannot be termed primary, because the conclusion is not drawn from primary principles as premisses.
The first species, then, of the different kinds of questions, which are three, has been exhibited,—I mean that, in which the essence being known, some one of its powers or properties is unknown. The second variety of propositions was that in which we all know the powders and properties, but do not know the essence; as, for example, in what part of the body is the principal faculty of the soul.
CHAPTER V.
APPLICATION OF DEMONSTRATION TO SCEPTICAL SUSPENSE OF JUDGMENT.
Now the same treatment which applies to demonstration applies also to the following question.
Some, for instance, say that there cannot be several originating causes for one animal. It is impossible that there can be several homogeneous originating causes of an animal; but that there should be several heterogeneous, is not absurd.
Suppose the Pyrrhonian suspense of judgment, as they say, [the idea] that nothing is certain: it is plain that, beginning with itself, it first invalidates itself. It either grants that something is true, that you are not to suspend your judgment on all things; or it persists in saying that there is nothing true. And it is evident, that first it will not be
