the whole—a rational, mortal, terrestrial, walking, laughing animal. For the things added by way of difference to the definition are the signs of the properties of things; but do not show the nature of the things themselves. Now they say that the difference is the assigning of what is peculiar; and as that which has the difference differs from all the rest, that which belongs to it alone, and is predicated conversely of the thing, must in definitions be assumed by the first genus as principal and fundamental.
Accordingly, in the larger definitions the number of the species that are discovered are in the ten Categories; and in the least, the principal points of the nearest species being taken, mark the essence and nature of the thing. But the least consists of three, the genus and two essentially necessary species. And this is done for the sake of brevity.
We say, then, Man is the laughing animal. And we must assume that which pre-eminently happens to what is defined, or its peculiar virtue, or its peculiar function, and the like.
Accordingly, while the definition is explanatory of the essence of the thing, it is incapable of accurately comprehending its nature. By means of the principal species, the definition makes an exposition of the essence, and almost has the essence in the quality.
CHAPTER VII.
ON THE CAUSES OF DOUBT OR ASSENT.
The causes productive of scepticism are two things principally. One is the changefulness and instability of the human mind, whose nature it is to generate dissent, either that of one with another, or that of people with themselves. And the second is the discrepancy which is in things; which, as to be expected, is calculated to be productive of scepticism.
For, being unable either to believe in all views, on account of their conflicting nature; or to disbelieve all, because that which says that all are unreliable is included in the
