In answer to the question put by Sokrates--What is Knowledge or Cognition? Theætêtus at first replies--That there are many and diverse cognitions:--of geometry, of arithmetic, of arts and trades, such as shoemaking, joinery, &c. Sokrates points out (as in the Menon, Hippias Major, and other dialogues) that such an answer involves a misconception of the question: which was general, and required a general answer, setting forth the characteristic common to all cognitions. No one can know what cognition is in shoemaking or any particular case--unless he first knows what is cognition generally.[3] Specimens of suitable answers to general questions are then given (or of definition of a general term), in the case of clay--and of numbers square and oblong.[4] I have already observed more than once how important an object it was with Plato to impress upon his readers an exact and adequate conception of the meaning of general terms, and the proper way of defining them. For this purpose he brings into contrast the misconceptions likely to arise in the minds of persons not accustomed to dialectic. [Footnote 3: Plato, Theætêt. p. 147 A. [Greek: Ou)d' a)/ra e)pistê/mên u(podêma/tôn suni/êsin, o( e)pistê/mên mê\ ei)dio/s? Ou) ga/r.]] [Footnote 4: Plato, Theætêt. p. 148. Oblong ([Greek: promê/keis]) numbers are such as can be produced only from two unequal factors. The explanation of this difficult passage, requiring us to keep in mind the geometrical conception of numbers usual among the Greek mathematicians, will be found clearly given in Mr. Campbell's edition of this dialogue, pp. 20-22.] [Side-note: Preliminary conversation before the second answer is given. Sokrates describes his own peculiar efficacy--mental obstetric--He cannot teach, but he can evolve knowledge out of pregnant minds.]