Stopper on Nasti's Contention and Stoic Logic

Abstract

In a recent critical notice, M. R. Stopper discusses at length what he calls 'Nasti's contention' (namely, the claim that the so-called Chrysippean implication is at least as strong as necessary equivalence between the consequent and its antecedent).' He casts some (reasonable) doubts on its real status, asking himself whether the contention is entailed or not by a well-known property of Stoic conditionals (namely that a conditional is sound (hugies) iff the negation of the consequent conflicts with its antecedent) when that property is conjoined with a statement disclosed by a Sextan passage (namely that 'according to them' i.e. to the Dogmatists as Sextus says, 'it is impossible for a sound conditional to be constituted from conflicting propositions': adunaton de esti [. . .J sunestos, PH II 189). According to Stopper, that statement is not a piece of Stoic logic but a consequence of a Sextan fallacy. In what follows I will argue that, although the statement disclosed by Sextus' passage may well be a piece of Stoic logic, Nasti's contention may need to be modified in order to get a better agreement with textual evidence.