Stoic vs. Aristotelian Syllogistic

At least since Lukasiewicz's paper "Zur Geschichte der Aussagenlogik" (Erkenntnis, 5, 1935, p. 111 ff.) historians of logic have usually contrasted Stoic and Aristotelian syllogistic äs the ancient forms of propositional logic and termor class-logic respectively. One may have serious misgivings about the way this usually is interpreted and argued for. In fact, one could argue that, to contrast the two Systems in this way, we would have to introduce many qualifications and explanations; indeed, so many qualifications that one may wonder whether it was not misleading to say that the relation between the two Systems was that between propositional logic and term-logic. There can be no doubt, in any case, that the Stoa and the Peripatus did not think that the difference between their logical Systems was that between propositional logic and term-logic. For otherwise one would expect the Aristotelians to treat Stoic logic äs a welcome and necessary complement to their doctrine of the categorical syllogism, and expect the Stoics in turn to regard Aristotelian syllogistic at least äs a welcome Supplement to their own hypothetical syllogistic. Yet the evidence we have suggests not only that both schools restricted their interest to their own logic but even that they rejected each other's syllogistic in some sense we will have to specify. It is some aspects of this apparent rivalry between the two doctrines which I will try to discuss in this paper. There would be little to discuss if we accepted Bochenski's explanation of this rivalry (Ancient Formal Logic, p. 81). Bochenski thinks that the ancient logicians somehow noticed the radical difference between propositional logic and term-logic and that "this difference was even feit äs an Opposition". Hardly more illuminating is Lejewski's account (in Edward's Encyclopedia of Philosophy, s.v. Logic, History of, p. 520): "As a result of interschool enmities and jealousies there was at first no cooperation in logical research be-