Property they divide in four ways: for it is that which happens to some one species alone, though not to every (individual of that species), as to a man to heal, or to geometrize: that also which happens to a whole species, though not to that alone, as to man to be a biped: that again, which happens to a species alone, and to every (individual of it), and at a certain time, as to every man to become grey in old age: in the fourth place, it is that in which it concurs (to happen) to one species alone, and to every (individual of it), and always, as risibility to a man; for though he does not always laugh, yet he is said to be risible, not from his always laughing, but from being naturally adapted to laugh, and this is always inherent in him, in the same way as neighing in a horse. They say also that these are validly properties, 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.