EPISTEMOLOGY (1) (2) (3) (4) Persuasive; e.g ‘It is day’, ‘I am talking’ Unpersuasive; e.g ‘If it is dark, it is day’ Persuasive and unpersuasive; e.g philosophical paradoxes Neither persuasive nor unpersuasive; e.g ‘The number of all the stars is odd’ However, persuasiveness is not a guarantee of truth: the bent appearance of an oar in water is persuasive enough, but is a false impression for all that No doubt a man who is wise will resist the temptation to accept all persuasive appearances, and will restrict his assent to appearances that are not only persuasive but reasonable Thus, Posidonius tells us, in addition to oVering cognitive impressions as the criterion of truth, some older Stoics identiWed the criterion as being right reason (D.L 54) However, the matter is further complicated In addition to cognitive impressions there are reasonable impressions A Stoic, trapped by King Ptolemy Philopator into taking wax pomegranates for the genuine article, replied that he had given his assent not to the proposition that they were pomegranates, but to the proposition that it was reasonable (eulogon) to believe that they were A reasonable impression, he said, was compatible with falsehood (D.L 177) If so, it seems, the assessment of whether an appearance is or is not cognitive cannot be a matter of reason The early Stoics give us no further assistance in determining the identifying feature of cognitive impressions The weakness of the Stoic position was exposed by Arcesilaus, the head of the New Academy during the latter part of the third century He challenged the Stoic deWnition of a cognitive impression as ‘something stamped and impressed from something that is, exactly as it is’ Could there not be, he asked, a false impression indiscernible from a true one? Zeno agreed that if an impression was such that there could be a false one exactly like it, then (even if true) it could not be a cognitive impression Accordingly he modiWed the deWnition, adding ‘and of such a kind that it could not arise from what is not’ (Cicero, Acad 77; S.E., M 251) But it is not clear how the Stoics were to establish in which cases such unmistakable distinguishing marks were to be found, or respond to a sceptical claim that wherever there was a true appearance a false indiscernible replica could be imagined 172