BOOK I. VII. 5-13
To state the true, to eliminate the false, to suspend judgement in doubtful cases. Is it enough, then, to learn this alone?—It is enough, says one.—Is it, then, also enough for the man who wants to make no mistake in the use of money to be told the reason why you accept genuine drachmas and reject the counterfeit?—It is not enough.—What, then, must be added to this? Why, what else but the faculty that tests the genuine drachmas and the counterfeit and distinguishes between them? Wherefore, in reasoning also the spoken word is not enough, is it? On the contrary, is it not necessary to develop the power of testing the true and the false and the uncertain and of distinguishing between them?—It is necessary.—What else besides this is proposed in reasoning? Pray accept the consequence of what you have properly granted. 10Come, is it enough, then, in this case also merely to know that this particular thing is true? It is not enough, but one must learn in what way a thing follows as a consequence upon certain other things, and how sometimes one thing follows upon one, and at other times upon several conjointly. Is it not, then, necessary that a man should also acquire this power, if he is to acquit himself intelligently in argument, and is himself not only to prove each point when he tries to prove it, but also to follow the argument of those who are conducting a proof, and is not to be misled by men who quibble as though they were proving something? There has consequently arisen among us, and shown itself to be necessary, a science which deals with inferential arguments and with logical figures and trains men therein.
But of course there are times when we have
