ἔτι δὲ οἱ ἀπὸ τῆς στοάς ἔχονται τῆσδε τῆς διαιρέσεως. (Adversus mathemati-cos VII, 16)5
Those who have divided philosophy in a more complete way are those who say that one part of philosophy deals with φύσις, another part with ἦθος, and a third with λόγoς. Plato first pointed the way to this possible division of philosophy insofar as in his philosophy he treats of many things that deal with the world, many things that concern human being, and quite a lot about what pertains to speaking. But it was the disciples of Xenocrates and the students of Aristotle who most explicitly divided philosophy this way. The Stoics, too, still hold to this division.6
Kant still liked to invoke this threefold division, the way he does in the Preface to his Groundwork of the Metaphysics of Morals:
Ancient Greek philosophy was divided into three sciences: physics, ethics, and logic. This division is perfectly suitable to the nature of the subject, and there is no need to improve upon it except, perhaps, to add its principle, partly so as to ensure its completeness [5] and partly so as to be able to determine correctly the necessary subdivisions.7
Note that Kant emphasizes the appropriateness of this division to the subject matter: i.e., it is a division that ultimately comes to the fore, more or less clearly, in every philosophical investigation. And when Kant says that one needs “only” to add the principle, we should bear in mind that the task of doing so continues to be one of philosophy’s fundamental concerns, one that has not been answered to this day and, when you get right down to it, hasn’t even been clearly posed either as a project or as a question.
The preliminary clarification of the meaning of the word “logic” led to a preliminary orientation to a fundamental division of the philosophical disciplines. It also provided a first view of the regions of being to which this division and indeed the whole of philosophy are directed.
5. Xenocrates (396–314 bce) was roughly a contemporary of Aristotle, and a follower of Speusippos, the first leader of the Academy after Plato. He catalogued and systematized Platonic philosophy in a scholastic way, taking studies that once were lived and putting them into the fixed form of a wisdom that could be taught.
6. Cf. Diogenes Laertius: τῆς φιλοσοφίας ὁ λόγoς πρότερον μὲν ἦν μονοειδὴς ὡς ὁ φυσικός, δεύτερον δὲ Σωκράτης προσέθηκε τὸν ἠθικόν, τρίτον δὲ Πλάτων τὸν διαλεκτικόν, καὶ ἐτελεσιούργησε τὴν φιλοσοφίαν (III, 34). [“At first philosophical discourse was of one kind: the discussion of nature. In the second instance Socrates added the discussion of ethics, and thirdly Plato added dialectics, thereby completing (the contours of) philosophy.”]
7. [GM, p. 387 / tr. 1.]