Let us concede for the present discussion (continues Sokrates) that cognition of cognition is possible. Still how does this prove that there can be cognition of non-cognition? that a man can know both what he knows and what he does not know? For this is what we declared self-knowledge and temperance to be.[20] To have cognition of cognition is one thing: to have cognition of non-cognition is a different thing, not necessarily connected with it. If you have cognition of cognition, you will be enabled to distinguish that which is cognition from that which is not--but no more. Now the knowledge or ignorance of the matter of health is known by medical science: that of justice known by political science. The knowledge of knowledge simply--cognition of cognition--is different from both. The person who possesses this last only, without knowing either medicine or politics, will become aware that he knows something and possesses some sort of knowledge, and will be able to verify so much with regard to others. But _what_ it is that he himself knows, or that others know, he will not thereby be enabled to find out: he will not distinguish whether that which is known belong to physiology or to politics; to do this, special acquirements are needed. You, a temperate man therefore, as such, do not know _what_ you know and _what_ you do not know; you know the bare fact, _that_ you know and _that_ you do not know. You will not be competent to cross-examine any one who professes to know medicine or any other particular subject, so as to ascertain whether the man really possesses what he pretends to possess. There will be no point in common between you and him. You, as a temperate man, possess cognition of cognition, but you do not know any special _cognitum_: the special man knows his own special _cognitum_ but is a stranger to cognition generally. You cannot question him, nor criticise what he says or performs, in his own specialty--for of that you are ignorant:--no one can do it except some fellow _expert_. You can ascertain that he possesses some knowledge: but whether he possesses that particular knowledge to which he lays claim, or whether he falsely pretends to it, you cannot ascertain:--since, as a temperate man, you know only cognition and non-cognition generally. To ascertain this point, you must be not only a temperate man, but a man of special cognition besides.[21] You can question and test no one, except another temperate man like yourself. [Footnote 20: Plato, Charm. 169 D. [Greek: nu=n me\n tou=to xugchôrê/sômen, dunato\n ei)=nai gene/sthai e)pistê/mên e)pistê/mês--i)/thi dê\ ou)=n, ei) o(/, ti ma/lista dunato\n tou=to, ti/ ma=llon oi(=o/n te/ e)stin ei)de/nai a(/ te/ tis oi)=de kai\ a(\ mê/? tou=to ga\r dê/pou e)/phamen ei)=nai to\ gignô/skein au(to\n kai\ sôphronei=n.]]