James Adam, The Republic of Plato

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ff. In this section of the Republic, Plato ascribes the originating impulse of his intellectual discipline to the stimulus supplied by the self-contradictory evidence of sense-perception. On the connexion of this principle with earlier Greek philosophy see 523 C note, and on the aim and scope of Plato's theory of Education as a whole App. II.

ὡς ἱκανῶς κτλ. is taken by Krohn (Pl. Fr. p. 91) as excluding the possibility of Ideas of concrete things. Such an inference is unwarranted. ἱκανῶς, ‘adequately’ ‘satisfactorily’ (cf. E below), does not imply that sensation can apprehend everything there is to know about e.g. a finger, but merely that in the case of a finger etc., sensible perception is as a rule all that we demand: we are not impelled to summon νόησις to our aid. Even the perception of a finger may awaken the intelligence, and in such cases we shall be led to the Idea of finger (523 D note).

ὡς τῆς αἰσθήσεως κτλ. On αἰσθήσεως see 523 C note ποιούσης has been doubted by Ast, who conjectures νοούσης; “sed αἰσθήσεως non est νοεῖν” (Schneider). The Greek means ‘produces no sound result,’ “nichts zuverlässiges giebt” (Schneider): the product of sensation is, in such cases, ὕπουλον or νοσῶδες. For οὐδὲν ὑγιές metaphorically used cf. Phaed. 90 E and (with Schneider) Ar. Plut. 50, 355 (πρὸς ἀνδρὸς οὐδὲν ὑγιές ἐστ᾽ εἰργασμένου).

τὰ πόρρωθεν κτλ. readily suggest themselves to Glauco, for they were familiar examples of optical delusion in the Platonic school: cf. (for πόρρωθεν φαινόμενα) Prot. 356 C, Theaet. 191 B, infra X 602 C ff., and (for ἐσκιαγραφημένα) II 365 C note