Whence then,—for this was the question which you asked,—comes memory, if we perceive nothing, since we cannot recollect anything which we have seen unless we have comprehended it? What? Did Polyænus, who is said to have been a great mathematician, after he had been persuaded by Epicurus to believe all geometry to be false, forget all the knowledge which he had previously possessed? But that which is false cannot be comprehended as you yourselves assert. If, therefore, memory is conversant only with things which have been perceived and comprehended, then it retains as comprehended and perceived all that every one remembers. But nothing false can be comprehended; and Scyron recollects all the dogmas of Epicurus; therefore they are all true. For all I care, they may be; but you also must either admit that they are so, and that is the last thing in your thoughts, or else you must allow me memory, and grant that there is plenty of room for it, even if there be no comprehension or perception. What then is to become of the arts? Of what arts? of those, which of their own accord confess that they proceed on conjecture more than on knowledge; or of those which only follow what appears to them, and are destitute of that art which you possess to enable them to distinguish between truth and falsehood? But there are two lights which, more than any others, contain the whole case; for, in the first place, you deny the possibility of any man invariably withholding his assent from everything. But that is quite plain; since Panætius, almost the greatest man, in my opinion, of all the Stoics, says that he is in doubt as to that matter, which all the Stoics except him think absolutely certain, namely as to the truth of the auspices taken by soothsayers, and of oracles, and dreams, and prophecies; and forbears to express any assent respecting them. And why, if he may pursue this course concerning those matters, which the men of whom he himself learnt considered unquestionable, why may not a wise man do so too in all other cases? Is there any position which a man may either approve or disapprove of after it has been asserted, but yet may not doubt about? May you do so with respect to the sorites whenever you please, and may not he take his stand in the same manner in other cases, especially when without expressing his assent he may be able to follow a probability which is not embarrassed by anything? The second point is that you declare that man incapable of action who withholds his assent from everything. For first of all we must see in what assent consists. For the Stoics say that the senses themselves are assents; that desire comes after them, and action after desire. But that every thing is at an end if we deny perception.