  Łukasiewicz revolutionized the history of logic. He proposed to look at the history of logical ideas through the glasses of mathematical logic. The reason was that he was convinced about the continuity of formal logic from Aristotle to modern mathematical logic, perhaps with a break from the 16th century to Boole and Frege (of course, with the exception of Leibniz). Thus, old sound logical theories should be considered as anticipations of ideas advanced in the 19th and the 20th centuries. Guided by this assumption, Łukasiewicz showed that the Stoics invented propositional calculus, contrary to the prevailing view that Stoic logic was a part of Aristotle’s logic. In particular, Łukasiewicz demonstrated that the Stoic logic of propositions was a system of rules, not theorems. Another of Łukasiewicz’s historical discoveries consisted in the rehabilitation of medieval logic, commonly neglected as fruitless scholasticism. He was joined in these investigations by Bocheński and Salamucha.