Having enunciated this definition, as one learnt from another person not named, Sokrates proceeds to examine and confute it. It rests on the assumption (he says), that the primordial elements are themselves unknowable; and that it is only the aggregates compounded of them which are knowable. Such an assumption cannot be granted. The result is either a real sum total, including both the two component elements: or it is a new form, indivisible and uncompounded, generated by the two elements, but not identical with them nor including them in itself. If the former, it is not knowable, because if neither of the elements are knowable, both together are not knowable: when you know neither A nor B you cannot know either the sum or the product of A and B. If the latter, then the result, being indivisible and uncompounded, is unknowable for the same reason as the elements are so: it can only be named by its own substantive name, but nothing can be predicated respecting it.[125] [Footnote 125: Plato, Theæt. pp. 203-206.] Nor can it indeed be admitted as true--That the elements are unknowable, and the compound alone knowable. On the contrary, the elements are more knowable than the compound.[126] [Footnote 126: Plato, Theæt. p. 206.] [Side-note: Rational explanation may have one of three different meanings. 1. Description in appropriate language. 2. Enumeration of all the component elements in the compound. In neither of these meanings will the definition of Cognition hold.] When you say (continues Sokrates) that knowledge is true opinion coupled with rational explanation, you may mean by _rational explanation_ one of three things. 1. The power of enunciating the opinion in clear and appropriate words. This every one learns to do, who is not dumb or an idiot: so that in this sense true opinion will always carry with it rational explanation.--2. The power of describing the thing in question by its component elements. Thus Hesiod says that there are a hundred distinct wooden pieces in a waggon: you and I do not know nor can we describe them all: we can distinguish only the more obvious fractions--the wheels, the axle, the body, the yoke, &c. Accordingly, we cannot be said to know a waggon: we have only a true opinion about it. Such is the second sense of [Greek: lo/gos] or rational explanation. But neither in this sense will the proposition hold--That knowledge is right opinion coupled with rational explanation. For suppose that a man can enumerate, spell, and write correctly, all the syllables of the name _Theætêtus_--which would fulfil the conditions of this definition: yet, if he mistakes and spells wrongly in any other name, such as _Theodôrus_, you will not give him credit for knowledge. You will say that he writes _Theætêtus_ correctly, by virtue of right opinion simply. It is therefore possible to have right opinion coupled with rational explanation, in this second sense also,--yet without possessing knowledge.[127]