§2.2.14Πρὸς δὲ τὸ ἔχειν τὰ προβλήματα ἐκλέγειν δεῖ τάς τε ἀνατομάς καὶ τὰς διαιρέσεις, οὕτω δὲ ἐκλέγειν, ὑποθέμενον τὸ γένος τὸ κοινὸν ἀπάντων, οἷον εἰ ζῷα εἴη τὰ τεθεωρημένα, ποῖα παντὶ ξῴῳ ὑπάρχει, ληφθέντων δὲ τούτων, πάλιν τῶν· λοιπῶν τῷ τπρώτῳ ποῖα παντὶ ἕπεται, οἷον εἰ τοῦτο ὄρνις, ποῖα παντὶ ἕπεται ὄρνιθι, καὶ οὕτως αἰεὶ τῷ ἐγύτατα·
In order to have problems, one must select both anatomical diagrams and divisions; and one must select them in this way, assuming the common genus of all—for example, if the things under consideration were animals, what properties belong to every animal, and when these are taken, again what properties follow every one of the first of the remaining terms—for example, if this is a bird, what properties follow every bird, and in this way always for the nearest term.
δῆλον γὰρ ὅτι ἕξομεν ἤδη λέγειν τὸ διὰ τί ὑπάρχει τὰ ἑπόμενα τοῖς ὑπὸ τὸ κοινόν, οἶον διὰ τί ἀνθρώπῳἢ ἵππῳ ὑπάρχει.
For it is clear that we shall then be able to state why the properties that follow belong to those under the common term, for example, why they belong to man or to horse.
ἔστω δὲ ξῷον ἐφʼ οὗ Α, τὸ δὲ Β τὰ ἑπόμενα παντὶ ζῴῳ, ἐφʼ ὧ δὲ Γ Ε τὰ τινὰ ῷα.
Let animal be that on which there is A, B be the properties following every animal, and Γ, Δ, Ε be certain particular animals.
δῆλον δὴ διὰ τί τὸ Β ὑπάρχει τῷ Δ διὰ γὰρ τὸ Α. μούως δὲ καὶ τοῖς ἄλλοις·
It is clear, then, why B belongs to Δ: for it is because of A.
καὶ ἀεὶ ἐπὶ τῶν κάτω ὁ αὐτὸς λόγος.
And likewise also for the others; and the same account always holds for the lower terms.
Νῦν μὲν οὖν κατὰ τὰ παραδεδομένα κοινὰ ὀνόματαε ἀέγομεν, δεῖ δὲ μὴ μόνον ἐπὶ τούτων σκοηεῖν, ἀλλὰ καὶ ἄν ἄλλο τι ὀφθῇ ὑπάρχον κοινόν, ἐκλαμβάνοντα, εἶτα τίσι τοῦτʼ ἀκολουθεῖ καὶ ποῖα τούτῳ ἕπεται, οἶον τοῖς κέρατα ἔχουσι τὸ ἔχειν ἐχῖνον, τὸ μὴ ἀμφώδοντʼ εἶναι· πάλιν τὸ κέρατʼ ἔχειν τίσιν ἕπεται.
Now, indeed, we speak according to the handed-down common names, but we must not only consider these, but also, if any other common feature is observed to belong, we must select it, and then look at what things this follows and what things follow it—for example, to those having horns there follows having an omasum and not having teeth in both jaws; and again, what things having horns follows.
δῆλον γὰρ διὰ τί ἐκείνοις ὑπάρξει τὸ εἰρημένον· διὰ γὰρ τὸ κέρατʼ ἔχειν ὑπάρξει.
For it will be clear why the aforementioned feature belongs to them: for it will belong to them because of having horns.
Ἔτι δʼ ἄλλος τρόπος ἐστὶ κατὰ τὸ ἀνάλογον ἐκλέγειν.
Moreover, there is another way, which is to select according to analogy.
ἕν γὰρ λαβεῖν οὐκ ἔστι τὸ αὐτό, ὃ δεῖ καλέσαι σηπίον καὶ ἄκανθαν καὶ ὀστοῦν· ἔσται δʼ ἑπόμενα καὶ τούτοις ὥσπερ μιᾶς τινος φύσεως τῆς τοιαύτης οὔσης.
For it is not possible to grasp one and the same thing which one should call cuttlebone, spine, and bone; yet there will be properties that follow these as well, as if there were some single nature of this kind.
§2.2.15Τὰ δʼ αὐτὰ προβλήματά ἐστι τὰ μὲν τῷ τὸ αὐτὸ μέσον ἔχειν, οἶον ὅτι πάντα ἀντιπερίστασις.
And the same problems are, on the one hand, those that have the same middle term, for example, that all are mutual replacement (antiperistasis).
τοίων δʼ ἔνια τῷ γένει ταὐτά, ὅσα ἔχει διαφορὰς τῷ ἄλλων ἢ ἄλλως εἶναι, οἷον διὰ τί ἠχεῖ, ἢ διὰ τί ἐμφαίνεται, καὶ διὰ τί ἶρίς· ἅπόντα γὰρ ταῦτα τὸ αὐτὸ πρόβλημά ἐστι γένει (πάντα γὰρ ἀνάκλασις), ἄλλʼ εἴεδι ἕτερα.
And some of these are the same in genus, namely, those which have differences by being of other things or in different ways—for example, why there is an echo, or why there is a reflection, and why there is a rainbow; for all these are the same problem in genus (for all are reflection), but different in species.
τὰ δὲ τῷ τὸμέσον ὑπὸ τὸ ἕτερον μέσον εἶναι διαφέρει τῶν προβλημάτων, οἶον διὰ τί ὁ Νεῦλος φθίνοντος τοῦ μηνὸς μᾶλλον ῥεῖ;
On the other hand, other problems differ by having one middle term under another middle term, for example, why does the Nile flow more when the month is waning?
διότι χειμεριώτερος φθίνων ὁ μείς.
Because the waning month is more wintry.
διὰ τί δὲ χειμεριώτερος φθίνων;
And why is the waning month more wintry?
διότι ἡ σελήνη ἀπολείπει.
Because the moon fails.
ταῦτα γὰρ οὕτως ἔχει πρὸς ἄλςτμια.
For these are related to each other in this way.