Stephen Read HUGH MACCOLL AND THE ALGEBRA OF STRICT IMPLICATION

C. I. Lewis repeatedly exempts MacColl from criticisms of his predecessors in their accounts of implication. They had all taken a true implication, or conditional, to be one with false antecedent or true consequent. MacColl uniquely, and correctly in Lewis’ view, rejected this account, identifying a true implication with the impossibility of true antecedent and false consequent. Lewis’ development of the calculus of strict implication arises directly and explicitly out of MacColl’s work. A close analysis of MacColl’s calculatory methods, and summaries of his main theses, serve to show that MacColl’s modal logic is in fact the logic T introduced by Feys and von Wright many decades later, the smallest normal epistemic modal logic.