I say, then, if you affirm that an animal is what has the power of sensation and of moving itself from appetency, that an animal is not simply what moves through appetency and is possessed of sensation. For it is also capable of sleeping, or, when the objects of sensation are not present, of not exercising the power of sensation. But the natural power of appetency or of sensation is the mark of an animal. For something of this nature is indicated by these things. First, if the fœtus is not capable of sensation or motion from appetency; which is the point proposed for consideration. Another point is; if the fœtus is capable of ever exercising the power of sensation or moving through appetency. In which sense no one makes it a question, since it is evident.
But the question was, whether the embryo is already an animal, or still a plant. And then the name animal was reduced to definition, for the sake of perspicuity. But having discovered that it is distinguished from what is not an animal by sensation and motion from appetency; we again separated this from its adjuncts; asserting that it was one thing for that to be such potentially, which is not yet possessed of the power of sensation and motion, but will some time be so, and another thing to be already so actually; and in the case of such, it is one thing to exert its powers, another to be able to exert them, but to be at rest or asleep. And this is the question.
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.
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 true. For it either affirms what is true or it does not affirm what is true. But if it affirms what is true, it concedes, though unwillingly, that something is true. And if it does not affirm what is true, it leaves true what it wished to do away with. For, in so far as the scepticism which demolishes is proved false, in so far the positions which are being demolished are proved true; like the dream which says that all dreams are false. For in confuting itself, it is confirmatory of the others.
And, in fine, if it is true, it will make a beginning with itself, and not be scepticism of anything else but of itself first. Then if [such a man] apprehends that he is a man, or that he is sceptical, it is evident that he is not sceptical. And how shall he reply to the interrogation? For he is evidently no sceptic in respect to this. Nay, he affirms even that he does doubt.