The suppression of Modus Ponens as a case of pragmatic preconditional reasoning

Abstract

The suppression of the Modus Ponens inference is described as a loss of confidence in the conclusion C of an argument ‘If A1 then C; If A2 then C; A1’ where A2 is a requirement for C to happen. It is hypothesised that this loss of confidence is due to the derivation of the conversational implicature ‘there is a chance that A2 might not be satisfied’, and that different syntactic introductions of the requirement A2 (e.g., ‘If C then A2’) will lead to various frequencies in the derivation of this implicature, according to previous studies in the field of causal explanation. An experiment is conducted, whose results support those claims. Results are discussed in the light of the Mental Logic and Mental Model theories, as well as in the light of the pragmatic approach to uncertain reasoning.