Property, indeed, is that which does not show what a thing is, but is present to it alone, and reciprocates with the thing. As it is the property of a man to be capable of grammar, for if he is a man he is capable of grammar, and if he is capable of grammar he is a man; since no one calls property that which may possibly be present with something else, as sleep to a man, not even if it should happen at a certain time to be present with him alone. If then any thing of this kind should be called property, it will not be called property simply, but at a certain time or with reference to something, since to be on the right hand is sometimes a property, but biped happens to be called property with reference to something, as to man with reference to horse and dog; but that nothing which may possibly be present with something else is reciprocally predicated is clear, since it is not necessary if any thing sleeps that it should be a man.
Genus, however, is that which is predicated of many things differing in species, in (answer to) what a thing is; but let those things be said to be predicated in (answer to) what a thing is, which are fitted to answer the person inquiring what the proposed thing is, as it is adapted to man, when it is asked what the proposed thing is, to say that he is animal. Moreover it is generic, whether one thing is in the same genus with another or in a different genus, since such a thing falls under the same method with genus, as having discussed that animal is the genus of man, and in like manner of ox, we shall reason that they are in the same genus; if, however, we should show that it is the genus of one of them, but not of the other, we shall reason that these are not in the same genus.
