EPISTEMOLOGY was gratuitous; but it is surely no more gratuitous than their own claim that true impressions are always liable to be confused with false replicas In fact, the Stoic reply seems to be either unnecessary or insuYcient, depending on how we interpret the sceptical challenge If only a genuine possibility of a mistake prevents an impression from being cognitive, then in order to preserve cognitive impressions the Stoic need not claim that in all cases a true impression will be irreplaceable by a false one: he need only claim that there are some cases in which this is so On the other hand, if the mere imaginability of a deceptive replica is suYcient to undermine the cognitivity of an impression, then the identity of indiscernibles will not restore it I may be as certain as I am of anything that I am talking to you: but isn’t it imaginable that you have an identical twin, quite unknown to me, and that it is he whom I am addressing? There are various degrees of scepticism A sceptic may simply be someone who denies the possibility of genuine knowledge (in some, or all, areas of inquiry) Such a sceptic need have no objection to the holding of beliefs on various topics, provided that the person holding them does not claim that those beliefs have the status of knowledge He may very well have a set of beliefs himself, including the belief that there is no such thing as knowledge There is no inconsistency here, provided he does not claim to know that there is no knowledge Arcesilaus went so far as to reprove Socrates for claiming to know that he knew nothing (Cicero, Acad 45) A more radical sceptic, however, may question not only the possibility of knowledge but also the propriety of belief He may recommend abstinence from not only the resolute assent characteristic of certainty, but also the tentative assent characteristic of opinion Arcesilaus appears to have been a sceptic of this kind: he maintained, Cicero tells us (Acad 44; LS 68a), ‘no one should assert or aYrm anything or oVer it assent; instead we should curb our rashness and hold it back from any slip It would be rash indeed to approve something false or unknown, and nothing is more disgraceful than to allow assent and approval to outrun cognition.’ Arcesilaus made a practice of oVering arguments pro and every thesis, so as to facilitate the suspension of assent that he recommended (Fin 10) Scholars are uncertain whether his arguments were all purely ad hominem or whether he did (inconsistently) assert as true his own sceptical philosophical position.7 See SchoWeld, in CHHP 334 174