[11] Plato, Sophist. p. 220 B. Νευστικοῦ μὴν τὸ μὲν πτηνὸν φῦλον ὁρῶμεν, τὸ δὲ ἔνυδρον.
It deserves notice that Plato here considers the air as a fluid in which birds swim.
[12] Plato, Sophist. pp. 219-221.
[13] Plato, Sophist. p. 221 A-B. Νῦν ἄρα τῆς ἀσπαλιευτικῆς — οὐ μόνον τοὔνομα, ἀλλὰ καὶ τὸν λόγον περὶ αὐτὸ τοὔργον, εἰλήφαμεν ἱκανῶς.
Such a lesson in logical classification was at that time both novel and instructive. No logical manuals then existed.
This is the first specimen which Plato gives of a systematic classification descending, by successive steps of bifurcation, through many subordinations of genera and species, each founded on a real and proclaimed distinction — and ending at last in an infima species. He repeats the like process in regard to the Sophist, the Statesman, and other professions to which he compares the one or the other: but it will suffice to have given one specimen of his method. If we transport ourselves back to his time, I think that such a view of the principles of classification implies a new and valuable turn of thought. There existed then no treatises on logic; no idea of logic as a scheme of mental procedure; no sciences out of which it was possible to abstract the conception of a regular method more or less diversified. On no subject was there any mass of facts or details collected, large enough to demand some regular system for the purpose of arranging and rendering them intelligible. Classification to a certain extent is of necessity involved, consciously or unconsciously, in the use of general terms. But the process itself had never been made a subject of distinct consciousness or reflection to any one (as far as our knowledge reaches), in the time of Plato. No one had yet looked at it as a process natural indeed to the human intellect, up to a certain point and in a loose manner, — but capable both of great extension and great improvement, and requiring especial study, with an end deliberately set before the mind, in order that it might be employed with advantage to regularise and render intelligible even common and well-known facts. To determine a series of descending classes, with class-names, each connoting some assignable characteristic — to distribute the whole of each class between two correlative sub-classes, to compare the different ways in which this could be done, and to select such membra condividentia as were most suitable for the purpose — this was in the time of Plato an important novelty. We know from Xenophon[14] that Sokrates considered Dialectic to be founded, both etymologically and really, upon the distribution of particular things into genera or classes. But we find little or no intentional illustration of this process in any of the conversations of the Xenophontic Sokrates: and we are farther struck by the fact that Plato, in the two dialogues which we are here considering, assigns all the remarks on the process of classification, not to Sokrates himself, but to the nameless Eleatic Stranger.
[14] Xenoph. Memor. iv. 5, 12.
Plato describes the Sophist as analogous to an angler. He traces the Sophist by descending subdivision from the acquisitive genus of art.
After giving the generic deduction of the angler from the comprehensive idea of Art, distributed into two sections, constructive and acquisitive, Plato proceeds to notice the analogy between the Sophist and an angler: after which he deduces the Sophist also from the acquisitive section of Art. The Sophist is an angler for rich young men.[15] To find his place in the preceding descending series, we must take our departure from the bisection — hunters of walking animals, hunters of swimming animals. The Sophist is a hunter of walking animals: which may be divided into two classes, wild and tame. The Sophist hunts a species of tame animals — men. Hunters of tame animals are bisected into such as hunt by violent means (robbers, enslavers, despots, &c.),[16] and such as hunt by persuasive means. Of the hunters by means of persuasion there are two kinds: those who hunt the public, and those who hunt individuals. The latter again may be divided into two classes: those who hunt to their own loss, by means of presents, such as lovers, &c., and those who hunt with a view to their own profit. To this latter class belongs the Sophist: pretending to associate with others for the sake of virtue, but really looking to his own profit.[17]
[15] Plato, Sophist. p. 222 A.