Sokrates proceeds to illustrate the position, just laid down, by cross-examining Menon's youthful slave, who, though wholly untaught and having never heard any mention of geometry, is brought by a proper series of questions to give answers out of his own mind, furnishing the solution of a geometrical problem. The first part of the examination brings him to a perception of the difficulty, and makes him feel a painful perplexity, from which he desires to obtain relief:[17] the second part guides his mind in the efforts necessary for fishing up a solution out of its own pre-existing, but forgotten, stores. True opinions, which he had long had within him without knowing it, are awakened by interrogation, and become cognitions. From the fact that the mind thus possesses the truth of things which it has not acquired in this life, Sokrates infers that it must have gone through a pre-existence of indefinite duration, or must be immortal.[18] [Footnote 17: Plato, Menon, p. 84 C. [Greek: Oi)/ei ou)=n a)\n au)to\n pro/teron e)picheirê=sai zêtei=n ê)\ mantha/nein tou=to o(\ ô)=|eto ei)de/nai ou)k ei)dô/s, pri\n ei)s a)pori/an kate/pesen ê(gêsa/menos mê\ ei)de/nai, kai\ e)po/thêse to\ ei)de/nai? Ou)/ moi dokei=. Ô)/nêto a)/ra narkê/sas?]] [Footnote 18: Plato, Menon, p. 86. [Greek: Ou)kou=n ei) a)ei\ ê( a)lê/theia ê(mi=n tô=n o)/ntôn e)sti\n e)n tê=| psuchê=|, a)tha/natos a)\n ê( psuchê\ ei)/ê?]] [Side-note: Enquiry taken up--Whether virtue is teachable? without determining what virtue is.] The former topic of enquiry is now resumed: but at the instance of Menon, the question taken up, is not--"What is virtue?" but--"Is virtue teachable or not?" Sokrates, after renewing his objection against the inversion of philosophical order by discussing the second question without having determined the first, enters upon the discussion hypothetically, assuming as a postulate, that nothing can be taught except knowledge. The question then stands thus--"Is virtue knowledge?" If it be, it can be taught: if not, it cannot be taught.[19] [Footnote 19: Plato, Menon, p. 87.] [Side-note: Virtue is knowledge--no possessions, no attributes, either of mind or body, are good or profitable, except under the guidance of knowledge.] Sokrates proceeds to prove that virtue is knowledge, or a mode of knowledge. Virtue is good: all good things are profitable. But none of the things accounted good are profitable, unless they be rightly employed; that is, employed with knowledge or intelligence. This is true not only of health, wealth, beauty, strength, power, &c., but also of the mental attributes justice, moderation, courage, quick apprehension, &c. All of these are profitable, and therefore good, if brought into action under knowledge or right intelligence; none of them are profitable or good, without this condition--which is therefore the distinctive constituent of virtue.[20] [Footnote 20: Plato, Menon, p. 89.]