Plato refutes the doctrine,[138] but in a manner not so much to prove its untruth, as to present it for a verbal incongruity. How can you properly say (he argues) that you _know_ the compound AB, when you know neither A nor B separately? Now it may be incongruous to restrict in this manner the use of the words _know--knowledge_: but the distinction between the two cases is not denied by Plato. Antisthenes said--"I feel a simple sensation (A or B) and can name it, but I do not _know_ it: I can affirm nothing about it in itself, or about its real essence. But the compound AB I do know, for I know its essence: I can affirm about it that _it is_ compounded of A and B, and this is its essence." Here is a real distinction: and Plato's argument amounts only to affirming that it is an incorrect use of words to call the compound _known_, when the component elements are not known. Unfortunately the refutation of Plato is not connected with any declaration of his own counter-doctrine, for Theætêtus ends in a result purely negative. [Footnote 138: Plato, Theætêt. ut suprâ.] [Side-note: Remarks of Aristotle upon the same.] Aristotle, in his comment on the opinion of Antisthenes, makes us understand better what it really is:--"Respecting simple essences (A or B), I cannot tell what they really are: but I can tell what they are like or unlike, _i.e._, I can compare them with other essences, simple or compound. But respecting the compound AB, I can tell what it really is: its essence is, to be compounded of A and B. And this I call _knowing_ or _knowledge_."[139] The distinction here taken by Antisthenes (or by his followers) is both real and useful: Plato does not contest it: while Aristotle distinctly acknowledges it, only that among the simple items he ranks both Percepta and Concepta. [Footnote 139: Aristot. Metaphys. [Greek: Ê]. 1043, b. 24-32, with the Scholia, p. 774, b. Br.