Arcesilas was quite right in admitting this. An addition was made to the definition; namely, That nothing false could be perceived; nor anything true either, if it was of such a character as that which was false. But he applied himself diligently to these discussions, in order to prove that no perception originated in what was true of such a kind that there might not be a similar one originating in what was false. And this is the one subject of controversy which has lasted to this day. For the other doctrine, that the wise man would never assent to anything, had nothing to do with this question. For it was quite possible for a man to perceive nothing, and nevertheless to be guided at times by opinion; which is said to have been admitted by Carneades. I, indeed, trusting rather to Clitomachus than to Philo or Metrodorus, believe that he argued this point rather than that he admitted it.
XXV. However, let us say no more about this. Undoubtedly, when opinion and perception are put an end to, the retention of every kind of assent must follow; as, if I prove that nothing can be perceived, you would then grant that a philosopher would never assent to anything. What is there then that can be perceived, if even the senses do not warn us of the truth? But you, O Lucullus, defend them by a common topic; and to prevent you from being able to do so it was, that I yesterday, when it was not otherwise necessary, said so much against the senses. But you say that you are not at all moved by "the broken oar" or "the dove's neck." In the first place, I will ask why?--for in the case of the oar, I feel that that which appears to be the case, is not really so; and that in the dove's neck there appear to be many colours, but are not in reality more than one. Have we, then, said nothing more than this? Let all our arguments stand: that man is tearing his cause to pieces; he says that his senses are voracious. Therefore you have always one backer who will plead the cause at his own risk: for Epicurus brings the matter down to this point, that if once in a man's life one of his senses has decided wrongly, none of them is ever to be trusted. This is what he calls being true, and confiding in his own witnesses, and urging his proofs to their just conclusion; therefore Timagoras the Epicurean declares, that when he had twisted his eye with his hand, he had never seen two flames appear out of one candle: for that the error was one of opinion, and not one of his eyes; just as if the question were what the fact is, and not what it appears to be. However, he is just like his predecessors. But as for you, who say that of the things perceived by your senses, some are true and some false, how do you distinguish between them? Cease, I beg of you, to employ common topics: we have plenty of them at home.