Aristotelis Opera (Bekker Edition, Vol. 2): Metaphysica, Ethica, Politica, Rhetorica, Poetica

9 The genus and the proprium property have in common that they are predicated equally of their species; for if man, then animal, and if man, then capable of laughter. The genus is predicated equally of the species, and the property of the individuals that participate in it; for both man and ox are animal in the same way, and Anytus and Meletus are capable of laughter. It is also common that the genus is predicated synonymously of its proper species, and the property of those things of which it is a property. They differ in that the genus is prior and the property is posterior; for one must be an animal, then be divided by differences into properties. And the genus is predicated of more species than those of which it is the genus, while the property is predicated of one species of which it is a property. And the property is predicated reciprocally; for of that which it is a property, the genus is not predicated reciprocally; for if it is an animal, it is a man, or if it is an animal, it is capable of laughter; but if it is a man, it is capable of laughter, and vice-versa. Furthermore, the property belongs to every species of which it is a property, always and only, while the genus belongs to every species of which it is a genus, always, but not only. Furthermore, properties are removed along with the removal of the genera, and genera are removed along with the removal of the species of which they are properties, so that when those of which they are properties are removed, they are removed along with them.

10 The genus and the accidens accident have in common that they are predicated of many, as has been said, whether they be separable or inseparable; "being moved" is predicated of many, and "black" of crows, Ethiopians, and certain birds. They differ in that the genus is prior to the species, but accidents are posterior to the species; even if you take an inseparable accident, the subject to which the accident happens is naturally prior. And the genus is shared equally by those who participate in it always, while the accident is not shared equally; for the participation in accidents admits of intensification and remission, while that of genera does not. And accidents exist primarily in the individuals, while genera and species are by nature prior to the individuals. And genera are predicated of those under them in the "what it is," while accidents are predicated in the "what kind of thing it is" or "how each is"; for if asked what kind of thing the Ethiopian is, you will say he is black, or how Socrates is, you will say he is sitting or walking.

11 How the genus differs from the other four has been stated, but it also happens that each of the other four differs from the others, so that since there are five, and each of the four differs from the others, four times five makes twenty differences in all. But it is not so; rather, by counting them successively, those two are left behind by one difference because it has already been taken, those three by two, those four by three, those five by four; ten differences in all are produced: four, three, two, one. How the genus differs from the differentia, from the species, from the property, and from the accident has been stated; these are four differences. How the differentia differs from the genus has been stated, and how the genus differs from it has been stated. It remains to be said how it differs from the species, the property, and the accident; these are three. Again, how the species differs from the differentia has been stated, and how the differentia differs from the species has been told; how the species differs from the genus has been stated, and how the genus differs from the species has been told. It remained to say how the species differs from the property and from the accident; these are two differences. How the property differs from the accident will be grasped; for how

it differs from the species, from the differentia, and from the genus has been stated beforehand in the difference of those things toward them. Of the four differences taken, the genus toward the others, three of the differentia, two of the species, and one of the property toward the accident, ten is the sum of all; of which we have already demonstrated the four that the genus has toward the others.

It is common to the differentia that it is shared equally; individual men share equally in the rational differentia. It is common that it is always present to those who participate; for Socrates is always rational, just as Socrates is always a man. It is a property of the differentia to be predicated in the "what kind of thing," while the species is in the "what it is"; even if "man" is taken as a "what kind of thing," it would not be a simple quality, but as the differences that came to the genus established it. Furthermore, the differentia is often observed in several species, as "four-footed" is in several animals that differ in species, while the species is only of the individuals under that species. Furthermore, the differentia is prior to the species derived from it; for the removal of the rational removes man, but the removal of man does not remove the rational, as the angel exists. Furthermore, the differentia is combined with another differentia (the rational was combined with the mortal for the constitution of man), but a species is not combined with a species in the same way, so as to produce another species; for a horse does not join with a donkey for the birth of a mule, but a horse simply combined would not produce a mule.

The differentia and the property have in common being shared equally by those who participate; for rational things share equally in the rational, as laughable things in the laughable. It is common to both that they are always present and present to all; even if a horse is maimed, it speaks toward the natural state, since the laughable is always had by the natural constitution, not by the act of laughing always. It is a property of the differentia that it is often spoken of in several species, such as "rational" in the angel and in man, while the property is in one species of which it is a property. The differentia is in those of which it is a differentia without converting, while properties are predicated reciprocally of those of which they are properties, because they convert.

The differentia and the accident have in common being spoken of in several, and it is common toward inseparable accidents that they are always and in all; for being two-footed is always present to all crows, and blackness likewise. They differ in that the differentia encompasses the species by which it is encompassed; for the rational encompasses man and the angel; accidents encompass in a certain way by being in many, but they are encompassed in a way by the fact that the subjects are capable of receiving not one accident, but many. The differentia is not subject to intensification or remission, while accidents admit of more and less. Opposite differences are mutually exclusive, but opposite accidents could sometimes coincide. So much for the commonalities and properties of the differentia and the others.

How the species differs from the genus and the differentia has been told where we were saying how the genus differs from the others and how the differentia differs from the others. It remains to show how it differs from the property and the accident.