 The Skeptics responded by denying the existence of cognitive impressions. According to Arcesilaus, “no impression arising from something true is such that an impression arising from something false could not also be just like it” (Cicero, 40D). So Arcesilaus denies that the third conjunct of the Stoic definition of the cognitive impression is ever satisfied. We can distinguish two specific tactics for denying this. First, the Skeptics point to cases of insanity. In his madness, Heracles had the impression that his children were, in fact, the children of his enemy Eurystheus and killed them. Since the impression must have been utterly convincing to him at the time at which he had it (judging by his subsequent action), it is clear from this that there can be false impressions which are indistinguishable from ones that are allegedly “stamped and impressed in accordance with that very thing” (Sextus Empiricus, 41H). Their second line of attack was to draw attention to objects which are so similar as to be indistinguishable (so that a completely accurate impression from one would be indistinguishable from one from the other). The story is related (Diog. Laert., 40F) that the Stoic philosopher Sphaerus (a student of Zeno’s) was tricked into thinking that wax pomegranates were real. This was again supposed to show that there could be impressions arising from what is not [sc. a pomegranate] which are indistinguishable from a cognitive impression.