Laws of language use and formal logic

After a review of recent work connected with Grice's maxims of conversation, special attention is paid to the principles related to the concept of informativeness. The operation of those principles constrains logic by limiting the meaning of logical particles and, more importantly, by contradicting axioms and many theorems of the propositional calculus. It is argued that, as the development of the individual's formal operations proceeds, a conflict with laws of language use arises. The notion of a conflict between two subsystems, logical and linguistic, is used in a developmental perspective to account, in a unified manner, for the observed discrepancy between subjects' behavior in deductive and inductive reasoning tasks and predictions based on formal logic.