[Footnote 38: Plato, Charm. 159 B, 160 D. [Greek: ê( sôphrosu/nê--tô=n kalô=n ti--e)n tô=| lo/gô=| tô=n kalô=n ti]. So also Sokrates in the Lachês (192 C), assumes that courage is [Greek: tô=n pa/nu kalô=n pragma/tôn], though he professes not to know nor to be able to discover what courage is.] [Footnote 39: See Gorgias, 462 B, 448 E; Menon, 70 B.] [Side-note: Different ethical points of view in different Platonic dialogues.] Among the various unsuccessful definitions of temperance propounded, there is more than one which affords farther example to show how differently Plato deals with the same subject in different dialogues. Here we have the phrase--"to do one's own business"--treated as an unmeaning puzzle, and exhibited as if it were analogous to various other phrases, with which the analogy is more verbal than real. But in the Republic, Plato admits this phrase as well understood, and sets it forth as the constituent element of justice; in the Gorgias, as the leading mark of philosophical life.[40] [Footnote 40: Plato, Republ. iv. 433, vi. 496 C, viii. 550 A; Gorgias, 526 C. Compare also Timæus, 72 A, Xen, Mem. ii. 9, 1.] [Side-note: Self-knowledge is here declared to be impossible.] Again, another definition given by Kritias is, That temperance consists in knowing yourself, or in self-knowledge. In commenting upon this definition, Sokrates makes out--first, that self-knowledge is impossible: next, that if possible, it would be useless. You cannot know yourself, he argues: you cannot know what you know, and what you do not know: to say that you know what you know, is either tautological or untrue--to say that you know what you do not know, is a contradiction. All cognition must be cognition of something distinct from yourself: it is a relative term which must have some correlate, and cannot be its own correlate: you cannot have cognition of cognition, still less cognition of non-cognition. [Side-note: In other dialogues, Sokrates declares self-knowledge to be essential and inestimable. Necessity for the student to have presented to him dissentient points of view.]