The Stromata, or Miscellanies

For the embryo is not to be called an animal from the fact that it is nourished; which is the allegation of those who turn aside from the essence of the question, and apply their minds to what happens otherwise. But in the case of all conclusions alleged to be found out, demonstration is applied 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 powers and properties, but do not know the essence; as, for example, in what part of the body is the principal faculty of the soul.