On Nelson’s conception of consistency

Abstract This paper scrutinizes Everett Nelson's conception of consistency by comparing it with the “standard” account of C. I. Lewis. This conflict surprisingly resembles a related controversy between the ancient logicians Chrysippus and Diodorus. Nelson's intuitions behind his peculiar conception of consistency are analysed and certain features of his logical system are critically examined. In particular, his objections against the law of the transitivity of implication and against the laws of conjunction and disjunction have to be discussed. Although Nelson's considerations contain interesting ideas in favour of a relevantist conception of logic, they fail to convincingly support the hardcore connexive thesis that even a selfcontradictory proposition doesn't entail its own negation.