 Strawson published his first book An Introduction to Logical Theory in 1952. In it he attempts to explain the nature, and the scope and limits, of formal logic. The eminence he had already achieved was reflected in the fact that it received a review by Quine in Mind. Strawson’s aim, generated in part by his reflections on the correct treatment of definite descriptions, is to say what formal logic is by explaining and elucidating its central concepts, among them the notion of entailment. Strawson favours explaining ‘P entails Q’ as ‘‘P and not Q’ is self-contradictory’, and explains or elucidates the notion of self-contradiction in terms of sentences saying nothing; in effect, they give and then take back simultaneously. Strawson then looks at the notion of form and of proof systems. He applies his ideas to traditional syllogistic logic as well as to modern propositional and predicate logic. It can be wondered how far his elucidation of the central notions is adequate, and it can also be wondered whether he attends to all the notions that need explanation in relation to formal logic (e.g., consistency and completeness). The main part of his book does not seem to have had a large influence on philosophers or logicians. However, three elements in his discussion had and continue to have considerable influence. First, he gave a fuller explanation of the notion of presupposition than he had previously provided. Second, Strawson asked how far the meaning of ordinary language connectives, such as ‘and’, ‘or’ and ‘if … then…’, can be equated with those of the truth functional connectives, such as ‘&amp;’, ‘∨’, and ‘→’, that logicians employ. Strawson argued that there are significant differences. His conclusion is that these ordinary expressions do not have what might be called a precise logic. The question that Strawson asked has continued to be central in the philosophy of language and has not been resolved. Grice took an opposite view to Strawson and part of the point of Grice’s account of implication, as opposed to meaning or saying, was to generate an explanation for the data that Strawson appealed to in arguing for a semantic difference between ordinary language and formal logic, without having to postulate a semantic difference. Strawson himself later criticised Grice’s theory, at least in relation to conditionals. Third, he proposed an approach to the problem of induction. We shall describe that later when looking at Strawson’s contribution to epistemology.