[Side-note: Criticism on the answer by Sokrates. Analogy of letters and words, primordial elements and compounds. Elements cannot be explained: compounds alone can be explained.] Taking up this definition, and elucidating it farther, Sokrates refers to the analogy of words and letters. Letters answer to the primordial elements of things; which are not matters either of knowledge, or of true opinion, or of rational explanation--but simply of sensible perception. A letter, or a primordial element, can only be perceived and called by its name. You cannot affirm of it any predicate or any epithet: you cannot call it _existing_, or _this_, or _that_, or _each_, or _single_, or by any other name than its own:[123] for if you do, you attach to it something extraneous to itself, and then it ceases to be an element. But syllables, words, propositions--_i. e._, the compounds made up by putting together various letters or elements--admit of being known, explained, and described, by enumerating the component elements. You may indeed conceive them correctly, without being able to explain them or to enumerate their component elements: but then you do not know them. You can only be said to know them, when besides conceiving them correctly, you can also specify their component elements[124]--or give explanation. [Footnote 123: Plato, Theæt. pp. 201 E--202 A. [Greek: au)to\ ga\r kath' au(to\ e(/kaston o)noma/sai mo/non ei)/ê, proseipei=n de\ ou)de\n a)/llo dunato/n, ou)/th' ô(s e)/stin, ou)/th' ô(s ou)k e)/stin' ê)/dê ga\r a)\n ou)si/an ê)\ mê\ ou)si/an au)tô=| prosti/thesthai, dei=n de\ ou)de\n prosphe/rein, ei)/per au)to\ e)kei=no mo/non tis e)rei=; e)pei\ ou)de\ to\ _au)to/_, ou)de/ to\ _e)kei=no_, ou)de\ to _e(/kaston_, ou)de\ to _mo/non_, ou)de\ to\ _tou=to_, prosoiste/on, ou)d' a)/lla polla\ toiau=ta; tau=ta me\n ga\r peritre/chonta pa=si prosphe/resthai, e(/tera o)/nta e(kei/nôn oi(=s prosti/thetai.] Also p. 205 C.] [Footnote 124: Plato, Theæt. p. 202.] [Side-note: Sokrates refutes this criticism. If the elements are unknowable, the compound must be unknowable also.]