We here see (what I have already adverted to in reviewing the Theagês, vol. ii. ch. xv. pp. 105-7) the character of mystery, unaccountable and unpredictable in its working on individuals, with which Plato invests the colloquy of Sokrates.] [Side-note: Ethical basis of the cross-examination of Sokrates--He is forbidden to pass by falsehood without challenge.] This passage, while it forcibly depicts the peculiar intellectual gift of Sokrates, illustrates at the same time the Platonic manner of describing, full of poetry and metaphor. Cross-examination by Sokrates communicated nothing new, but brought out what lay buried in the mind of the respondent, and tested the value of his answers. It was applicable only to minds endowed and productive: but for them it was indispensable, in order to extract what they were capable of producing, and to test its value when extracted. "Do not think me unkind," (says Sokrates,) "or my procedure useless, if my scrutiny exposes your answers as fallacious. Many respondents have been violently angry with me for doing so: but I feel myself strictly forbidden either to admit falsehood, or to put aside truth."[9] Here we have a suitable prelude to a dialogue in which four successive answers are sifted and rejected, without reaching, even at last, any satisfactory solution. [Footnote 9: Plato, Theætêt. p. 151 D.] [Side-note: Answer of Theætêtus--Cognition is sensible perception: Sokrates says that this is the same doctrine as the _Homo Mensura_ laid down by Protagoras, and that both are in close affinity with the doctrines of Homer, Herakleitus, Empedoklês, &c., all except Parmenides.] The first answer given by Theætêtus is--"Cognition is sensation (or sensible perception)". Upon this answer Sokrates remarks, that it is the same doctrine, though in other words, as what was laid down by Protagoras--"Man is the measure of all things: of things existent, that they exist: of things non-existent, that they do not exist. As things appear to me, so they are to me: as they appear to you, so they are to you."[10] Sokrates then proceeds to say, that these two opinions are akin to, or identical with, the general view of nature entertained by Herakleitus, Empedoklês, and other philosophers, countenanced moreover by poets like Homer and Epicharmus. The philosophers here noticed (he continues), though differing much in other respects, all held the doctrine that nature consisted in a perpetual motion, change, or flux: that there was no real Ens or permanent substratum, but perpetual genesis or transition.[11] These philosophers were opposed to Parmenides, who maintained (as I have already stated in a previous chapter) that there was nothing real except Ens--One, permanent, and unchangeable: that all change was unreal, apparent, illusory, not capable of being certainly known, but only matter of uncertain opinion or estimation. [Footnote 10: Plato, Theætêt. pp. 151 E--152 A.