 The Academics appealed to the skeptic’s stock in trade, dreams, madness, optical illusions and divinely inspired visions, in order to argue that the special character allegedly proper to cognitive impressions was not in fact peculiar to impressions produced in the required truth-guaranteeing way, but could also be found in false impressions (Cicero, Acad. 2.49–54, 79–82, 88–90; Sextus Empiricus, Adversus mathematicos [henceforwad S.E. M] 7.402–8 = Long and Sedley [henceforward L&amp;S] 40H). If so, impressions that arise in the specified conditions, though true, will be indistinguishable from false impressions—so far as any intrinsic, discriminable character is concerned. Therefore they will not be cognitive, and not being cognitive, they will not be able to serve as a criterion. That there are no cognitive impressions is the first of the two propositions most closely associated with ancient skepticism. And since it then follows, on Stoic assumptions, that nothing can be known, this was often taken to be equivalent to the claim that nothing can be known. The second skeptical proposition, that one ought to suspend judgment, the Academics deduced from the first together with the Stoic doctrine that the wise do not hold (mere) opinions (S.E. M 7.155–7 = L&amp;S 41C). On Stoic assumptions, assent to an impression that is not cognitive (either in the strict sense or in a broader sense which covers impressions that, though not perceptual, nonetheless afford an equally secure grasp of their contents), is sufficient to make the resulting judgment an opinion. Therefore, in the absence of cognitive impressions, one can avoid opinion only by suspending judgment entirely.