 A decisive event in Łukasiewicz’s development as an historian of logic was his discovery of ancient Stoic logic. It seems he was examining a dissertation on the Stoics and to prepare for it he read original texts. He thereupon discovered that Stoic logic, contrary to the then standard opinion, voiced by Prantl, Zeller and others, was not a bowdlerized and defective Aristotelian syllogistic, but an early propositional logic, so that for example the first Stoic indemonstrable, “if the first, then the second; but the first, therefore the second” is simply modus ponens or detachment for the conditional ‘if’, and the variables, represented not by letters but by ordinal numerals, are propositional variables, not term variables. He first voiced this view, which is now of course standard, at a meeting in Lwów in 1923. A more systematic treatment of 1934, “On the History of the Logic of Propositions”, is a delightful vignette taking in the broad sweep from the Stoics, ancient disputes about the meaning of the conditional, Petrus Hispanus and Ockham on the De Morgan laws, the medieval theory of consequences, and culminating with Frege and modern propositional calculi. Modern appreciation of the achievements of Stoic logic dates from Łukasiewicz’s clarification and his unstinting praise of the Stoics, especially Chrysippus. Łukasiewicz appreciated that Prantl did not have the benefit of knowing post-Fregean logic, and despite Prantl’s erroneous dismissal of the “stupidity” of much Stoic logic did at least provide helpful sources. Nevertheless, Łukasiewicz’s judgement on past historians of logic is scathing: