§10.8τὸ δʼ ἕτερον τῷ εἴδει τινὸς τὶ ἕτερόν ἐστι, καὶ δεῖ τοῦτο ἀμφοῖν ὑπάρχειν· οἷον εἰ ζῷον ἕτερον τῷ εἴδει, ἄμφω ζῷα.
That which is other in species is other than something in respect of something, and this must belong to both; for example, if an animal is other in species, both are animals.
ἀνάγκη ἄρα ἐν γένει τῷ αὐτῷ εἶναι τὰ ἕτερα τῷ εἴδει·
Therefore, those things that are other in species must be in the same genus.
τὸ γὰρ τοιοῦτο γένος καλῶ ὃ ἄμφω ἓν ταὐτὸ λέγεται, μὴ κατὰ συμβεβηκὸς ἔχον διαφοράν, εἴτε ὡς ὕλη ὂν εἴτε ἄλλως.
For I call such a thing a genus, which is said to be one and the same for both, having its difference not accidentally, whether existing as matter or otherwise.
οὐ μόνον γὰρ δεῖ τὸ κοινὸν ὑπάρχειν, οἷον ἄμφω ζῷα, ἀλλὰ καὶ ἕτερον ἑκατέρῳ τοῦτο αὐτὸ τὸ ζῷον, οἷον τὸ μὲν ἵππον τὸ δὲ ἄνθρωπον, διὸ τοῦτο τὸ κοινὸν ἕτερον ἀλλήλων ἐστὶ τῷ εἴδει.
For not only must the common belong [to both], e.g., both are animals, but also this very "animal" must be other for each of the two, e.g., the one a horse and the other a man; wherefore this common [property] is other in species from one another.
ἔσται δὴ καθʼ αὑτὰ τὸ μὲν τοιονδὶ ζῷον τὸ δὲ τοιονδί, οἷον τὸ μὲν ἵππος τὸ δʼ ἄνθρωπος.
It will indeed be in itself this kind of animal and that kind of animal, e.g., the one a horse and the other a man.
ἀνάγκη ἄρα τὴν διαφορὰν ταύτην ἑτερότητα τοῦ γένους εἶναι.
Therefore, this difference must be an otherness of the genus.
λέγω γὰρ γένους διαφορὰν ἑτερότητα ἣ ἕτερον ποιεῖ τοῦτο αὐτό.
For by a difference of the genus I mean an otherness which makes this very thing other.
ἐναντίωσις τοίνυν ἔσται αὕτη (δῆλον δὲ καὶ ἐκ τῆς ἐπαγωγῆς)· πάντα γὰρ διαιρεῖται τοῖς ἀντικειμένοις, καὶ ὅτι τὰ ἐναντία ἐν ταὐτῷ γένει, δέδεικται· ἡ γὰρ ἐναντιότης ἦν διαφορὰ τελεία, ἡ δὲ διαφορὰ ἡ εἴδει πᾶσα τινὸς τί, ὥστε τοῦτο τὸ αὐτό τε καὶ γένος ἐπʼ ἀμφοῖν (διὸ καὶ ἐν τῇ αὐτῇ συστοιχίᾳ πάντα τὰ ἐναντία τῆς κατηγορίας ὅσα εἴδει διάφορα καὶ μὴ γένει, ἕτερά τε ἀλλήλων μάλιστα—τελεία γὰρ ἡ διαφορά—καὶ ἅμα ἀλλήλοις οὐ γίγνεται).
This, then, will be a contrariety (and this is clear also from induction); for all things are divided by opposites, and it has been shown that contraries are in the same genus; for contrariety was complete difference, and every difference in species is a difference of something in respect of something, so that this same thing is also a genus for both (wherefore also all contraries in the same column of coordination of category, as many as are different in species and not in genus, are both most other than one another—for the difference is complete—and do not co-exist with one another).
ἡ ἄρα διαφορὰ ἐναντίωσίς ἐστιν.
Therefore, the difference is contrariety.
τοῦτο ἄρα ἐστὶ τὸ ἑτέροις εἶναι τῷ εἴδει, τὸ ἐν ταὐτῷ γένει ὄντα ἐναντίωσιν ἔχειν ἄτομα ὄντα (ταὐτὰ δὲ τῷ εἴδει ὅσα μὴ ἔχει ἐναντίωσιν ἄτομα ὄντα)· ἐν γὰρ τῇ διαιρέσει καὶ ἐν τοῖς μεταξὺ γίγνονται ἐναντιώσεις πρὶν εἰς τὰ ἄτομα ἐλθεῖν·
This, then, is what it is to be other in species: to have contrariety while being in the same genus and being indivisible (and those things are the same in species which, being indivisible, do not have contrariety); for in division and in intermediates, contrarieties arise before we come to the indivisibles.
ὥστε φανερὸν ὅτι πρὸς τὸ καλούμενον γένος οὔτε ταὐτὸν οὔτε ἕτερον τῷ εἴδει οὐθέν ἐστι τῶν ὡς γένους εἰδῶν (προσηκόντως· ἡ γὰρ ὕλη ἀποφάσει δηλοῦται, τὸ δὲ γένος ὕλη οὗ λέγεται γένος—μὴ ὡς τὸ τῶν Ἡρακλειδῶν ἀλλʼ ὡς τὸ ἐν τῇ φύσει), οὐδὲ πρὸς τὰ μὴ ἐν ταὐτῷ γένει, ἀλλὰ διοίσει τῷ γένει ἐκείνων, εἴδει δὲ τῶν ἐν ταὐτῷ γένει.
Hence it is clear that in relation to what is called the genus, none of the species as of the genus is either the same or other in species (and fittingly so; for matter is indicated by negation, and the genus is the matter of that of which it is called the genus—not in the sense of the Heraclidae but as that which is in nature), nor is it so in relation to things not in the same genus, but it will differ in genus from those, and in species from those in the same genus.
ἐναντίωσιν γὰρ ἀνάγκη εἶναι τὴν διαφορὰν οὗ διαφέρει εἴδει· αὕτη δὲ ὑπάρχει τοῖς ἐν ταὐτῷ γένει οὖσι μόνοις.
For the difference of that from which it differs in species must be a contrariety; and this belongs only to those things which are in the same genus.