They say also that [the latter] are properties in the strict sense, because they reciprocate, since if any thing be a horse it is capable of neighing, and if any thing be capable of neighing it is a horse.
[Accident.] Accident is that which is present and absent without the destruction of its subject. It receives a two-fold division, for one kind of it is separable, but the other inseparable, e.g., "to sleep" is a separable accident, but "to be black" happens inseparably to a crow and an Ethiopian; we may possibly indeed conceive a white crow, and an Ethiopian casting his colour, without destruction of the subject.
They also define it thus: "accident is that which may be present and not present to the same thing"; [they] also [define it as] "that which is neither genus, nor difference, nor species, nor property, yet is always inherent in a subject."
[Predication and the Predicables.] Having discussed all that were proposed, I mean, genus, species, difference, property, accident, we must declare what things are common, and what peculiar to them. Now it is common to them all to be predicated, as we have said, of many things, but genus (is predicated) of the species and individuals under it, and difference in like manner; but species, of the individuals under it; and property, both of the species, of which it is the property, and of the individuals under that species; again, accident (is predicated) both of species, and individuals. For "animal" is predicated of "horse" and "ox," which are species, and also of this particular horse and ox, which are individuals, but "irrational" is predicated of "horse" and "ox," and of individuals. Species however, as "man," is predicated of individuals alone, but property both of the species of which it is the property, and of the individuals under that species; as "risible" both of "man," and of individual men, but "black" of the species of crows, and of individuals, being an inseparable accident; and "moving," of "man" and "horse," being a separable accident. Notwithstanding, it is pre-eminently [predicated] of individuals, but secondarily of those things which comprehend individuals.