[21] Diog. L. ii. 106. Οὖτος ἒν τὸ ἀγαθὸν ἀπεφῄνατο πολλοῖς ὀνόμασι καλούμενον· ὅτε μὲν γὰρ φρόνησιν, ὅτε δὲ θεόν, καὶ ἄλλοτε νοῦν καὶ τὰ λοιπά. Τὰ δὲ ἀντικείμενα τῷ ἀγαθῷ ἀνῄρει, μὴ εἶναι φάσκων. Compare also vii. 2, 161, where the Megarici are represented as recognising only μίαν ἀρετὴν πολλοῖς ὀνόμασι καλουμένην. Cicero, Academ. ii. 42.
Doctrine of Eukleides about Bonum.
It was in this manner that Eukleides solved the problem which Sokrates had brought into vogue — What is the Bonum — or (as afterwards phrased) the Summum Bonum? Eukleides pronounced the Bonum to be coincident with the Ens Unum of Parmenides. The Parmenidean thesis, originally belonging to Transcendental Physics or Ontology, became thus implicated with Transcendental Ethics.[22]
[22] However, in the verse of Xenophanes, the predecessor of Parmenides — Οὗλος ὁρᾷ, οὗλος δὲ νοεῖ, οὗλος δέ τ’ ἀκούει — the Universe is described as a thinking, seeing, hearing God — Ἓν καὶ Πᾶν. Sextus Empir. adv. Mathemat. ix. 144; Xenophan. Fragm. p. 36, ed. Karsten.
The doctrine compared to that of Plato — changes in Plato.
Plato departs from Sokrates on the same point. He agrees with Eukleides in recognising a Transcendental Bonum. But it appears that his doctrines on this head underwent some change. He held for some time what is called the doctrine of Ideas: transcendental Forms, Entia, Essences: he considered the Transcendental to be essentially multiple, or to be an aggregate — whereas Eukleides had regarded it as essentially One. This is the doctrine which we find in some of the Platonic dialogues. In the Republic, the Idea of Good appears as one of these, though it is declared to be the foremost in rank and the most ascendant in efficacy.[23] But in the later part of his life, and in his lectures (as we learn from Aristotle), Plato came to adopt a different view. He resolved the Ideas into numbers. He regarded them as made up by the combination of two distinct factors:—1. The One — the Essentially One. 2. The Essentially Plural: The Indeterminate Dyad: the Great and Little. — Of these two elements he considered the Ideas to be compounded. And he identified the Idea of Good with the essentially One — τὸ ἀγαθὸν with τὸ ἕν: the principle of Good with the principle of Unity: also the principle of Evil with the Indeterminate. But though Unity and Good were thus identical, he considered Unity as logically antecedent, or the subject — Good as logically consequent, or the predicate.[24]
[23] Plato, Republic, vi. p. 508 E, vii. p. 517 A.
[24] The account given by Aristotle of Plato’s doctrine of Ideas, as held by Plato in his later years, appears in various passages of the Metaphysica, and in the curious account repeated by Aristoxenus (who had often heard it from Aristotle — Ἀριστοτέλης ἀεὶ διηγεῖτο) of the ἀκρόασις or lecture delivered by Plato, De Bono. See Aristoxen. Harmon. ii. p. 30, Meibom. Compare the eighth chapter in this work, — [Platonic Compositions Generally]. Metaphys. N. 1091, b. 13.τῶν δὲ τὰς ἀκινήτους οὐσίας εἶναι λεγόντων (sc. Platonici) οἱ μέν φασιν αὐτὸ τὸ ἓν τὸ ἀγαθὸν αὐτὸ εἶναι· οὐσίαν μέντοι τὸ ἓν αὐτοῦ ᾤοντο εἶναι μάλιστα, which words are very clearly explained by Bonitz in the note to his Commentary, p. 586: also Metaphys. 987, b. 20, and Scholia, p. 551, b. 20, p. 567, b. 34, where the work of Aristotle, Περὶ Τὰγαθοῦ, is referred to: probably the memoranda taken down by Aristotle from Plato’s lecture on that subject, accompanied by notes of his own.
In Schol. p. 573, a. 18, it is stated that the astronomer Eudoxus was a hearer both of Plato and of Eukleides.
The account given by Zeller (Phil. der Griech. ii. p. 453, 2nd ed.) of this latter phase of the Platonic doctrine of Ideas, applies exactly to that which we hear about the main doctrine of Eukleides. Zeller describes the Platonic doctrine as being “Eine Vermischung des ethischen Begriffes vom höchsten Gut, mit dem Metaphysischen des Absoluten: Der Begriff des Guten ist zunächst aus dem menschlichen Leben abstrahirt; er bezeichnet das, was dem Menschen zuträglich ist. So noch bei Sokrates. Plato verallgemeinert ihn nun zum Begriff des Absoluten; dabei spielt aber seine ursprüngliche Bedeutung noch fortwährend herein, und so entsteht die Unklarheit, dass weder der ethische noch der metaphysische Begriff des Guten rein gefasst wird.”