James Adam, The Republic of Plato

506B - 508B After some hesitation, Socrates undertakes to describe the Idea of Good, not as it is in itself, but through its image, analogue, or offspring.

Let me remind you (he proceeds) of our usual distinction between Particulars and Ideas, the former apprehended by Sight, the latter by Reason. In the case of most of the senses, nothing is required except the faculty and its object in order that a sensation may take place. But in order that we may see, a third requisite is necessary, viz. Light. Now the author of Light is the Sun, and we may therefore say that the Sun is the cause of Sight. We must not identify either Sight or the Eye with the Sun, although the Eye resembles the Sun more closely than any other organ of sense, and the Sun himself is seen by the Eye.

πότερον ἐπιστήμην κτλ. Even if it could be shewn that the Philebus is earlier than the Republic— and recent critics take the opposite view —there would be no sufficient reason for holding (with Zeller^{4} II 1. p. 708 note) that Plato is referring to that dialogue, although he there denies that either Knowledge or Pleasure is the Chief Good (20 B ff., 60 E). See also on 505 C and 506 E.

οὗτος κτλ. καλῶς has in reality— see cr. n.—more and better MS support than καλός, which Schneider retained in the belief that A read καλός. Used in this way, καλῶς is colloquial (Jebb on Soph. O. T. 1008 καλῶς ε<*> δῆλος οὐκ εἰδὼς τί δρᾷς).