περὶ ποίων κτλ.
On the derisive
ποῖος see 522 D
n. Mathematical units are in every case (
ἕκαστον) equal each to each (
πᾶν παντί), and destitute of parts; whereas
sensible units (e.g. one horse, one cow etc.) are
not equal to each other, and
are divisible. In
πᾶν παντί Plato copies the formal language of mathematics: cf.
ἑκατέραν ἑκατέρᾳ and the like in Euclid
passim. For the sense see
Phil. 56 C
ff., where these two kinds of number are made the basis of a distinction between philosophical or scientific and popular or unscientific
ἀριθμητική. It should be carefully noted that a plurality of mathematical units is expressly recognised both here (
ἴσον τε ἕκαστον πᾶν παντί κτλ.) and in
Phil. l. c. (
μονάδα μονάδος ἑκάστης τῶν μυρίων μηδεμίαν ἄλλην ἄλλης διαφέρουσαν). This entirely confirms what Aristotle tells us, viz. that Plato placed
μαφηματικά between
αἰσθητά and
εἴδη, τῷ τὰ μὲν πόλλ’ ἄττα ὅμοια εἶναι, τὸ δὲ εἶδος αὐτὸ ἓν ἕκαστον μόνον (
Met. A 6. 987^{b} 14 ff.). There are therefore three kinds of
μονάδες in Plato's scheme—the Ideal
μονάς, of which only one exists, the Mathematical and the Sensible, of each of which there are many. See on VI 510 D and App. I, where I have quoted further evidence on this subject, and endeavoured to explain the philosophical truth which is contained in the Platonic doctrine of mathematical numbers, magnitudes etc. as intermediates between the Ideas and sensibles.
ὧν κτλ.
ὧν is for
περὶ ὧν rather than
<*> (as J. and C. hold): cf. VI 510 D
οὐ περὶ τούτων διανοούμενοι, and (for the grammatical construction) III 402 A note
διανοηθῆναι should be understood in the technical sense of VI 511 E.
τῷ ὄντι ἀναγκαῖον
. Perhaps with a play on
προσαναγκάζον (J. and C.): see on
τῷ ὄντι VI 511 B.
ὀξεῖς κτλ.
Plato was very emphatic on this point: see
Laws 747 B and 819 C
φύονται was restored by Schneider from the best MSS. Earlier editions read
φαίνονται on inferior authority.
ἂν ‐‐ γυμνάσωνται κτλ.
Even Isocrates admits this, although his self-styled ‘Philosophy’ was something very different from Plato's: see
Antid. 265—266, especially
γυμνασίαν μέντοι τῆς ψυχῆς καὶ παρασκευὴν φιλοσοφίας καλῶ τὴν διατριβὴν τὴν τοιαύτην (mathematical studies).
ἅ γε μείζω κτλ.
is an important principle with Plato, who does not believe in any royal road to learning: cf. 530 C and VI 503 E. In antiquity, while algebra was still unknown,
ἀριθμητική must have taxed the powers of thought far more than now, and been, from the Platonic point of view, all the more valuable on that account as an educative discipline. The treatment of numbers by Euclid Books VII—X will illustrate Plato's observation: see Gow
Gk Math. pp. 74—85, with De Morgan's remarks there quoted.
ὡς τοῦτο
. ὡς=‘quam’ instead of
ἤ is found sporadically in Greek literature after comparatives: see my note on
Ap. 30 B
, 36 D. To say that in all such cases the comparative is equivalent to
οὕτω with the positive is only to shelve the difficulty; and it is better to recognise the usage as exceptional than summarily to dismiss it as a barbarism (with Thompson on
Gorg. 492 E
). J. and C. after
οὐδὲ πολλά supply
ἃ πόνον οὕτω μέγαν παρέχεται, but the ellipse is too difficult, especially as
οὐδὲ πολλά is only a kind of afterthought to or elaboration of
οὐ ῥᾳδίως.
τὸ ἐχόμενον τούτου
. If
γεωμετρία i.e.
ἡ τοῦ ἐπιπέδου (plane surfaces)
πραγματεία (528 D) concerns itself with
δευτέρα αὔξη, and Stereometry with
τρίτη αὔξη, we may infer that
ἀριθμητική deals with the
πρώτη αὔξη, i.e. presumably the line, which, according to the Pythagoreans, is a collection of points (cf.
Laws 894 A and Rothlauf l.c. p. 51). And in point of fact the line represented number among the Pythagoreans exactly as the point is the geometrical symbol for the unit: cf. IX 587 D note Hence
ἐχόμενον τούτου: we take the
δευτέρα αὔξη after the first. See also App. II to this Book, and App. I to Book VIII Part I § 2.
ἢ γεωμετρίαν κτλ.
The sequence —Geometry after
ἀριθμητική—was probably a usual one with teachers, even in Plato's time: see Grasberger
Erziehung u. Unterricht II p. 340 and cf. App. II.
ὅσον μὲν κτλ.
is exactly the attitude of the historical Socrates, as Krohn (
Pl. St. p. 376) and others have pointed out, comparing
Xen.
Mem. IV 7. 2
ff. Practical necessities of this kind probably originated the science (Gow
Gk Math. pp. 134 ff.) and gave it its name
γεωμετρία. The name
μαθήματα (or
μαθηματικά) in the special sense of Mathematics owes its origin, no doubt, to the position occupied by mathematical studies in Plato's
μαθήματα: but the usage itself is not found till Aristotle (Rothlauf l.c. p. 18), although it is clear from [
Epin.] 990 D, that some Platonists resented the
γελοῖον ὄνομα γεωμετρίαν. Glauco represents the practical point of view throughout: cf. 527 D.
καὶ πορείαις
. “Scriptum vellem
καὶ ἐν πορείαις” (Stallbaum). The idiom is common enough: see KühnerBlass
Gr. Gr. II 1, p. 548.
τὸ εὐδαιμονέστατον τοῦ ὄντος
is cited by Stumpf (l.c. p. 95 note 3) in support of his identification of the Idea of Good with God: see on VI 505 A.
γένεσιν
. 519 A note