 In his review, Prior approvingly quoted Łukasiewicz’s assertion that ‘the logic of the Stoics, the inventors of the ancient form of the propositional calculus, was much more important than all the syllogisms of Aristotle’ (Łukasiewicz 1951a: 131). In The Craft, propositional logic is barely mentioned until the final chapter, whereas Formal Logic begins with a thorough introduction to the subject. On page 3 of Formal Logic Prior stated that the logic of propositions is ‘basic, and the rest of logic built upon it’.