Monism: The One True Logic
Abstract
Logical pluralism is the claim that different accounts of validity can
be equally correct. Beall and Restall have recently defended this position. Validity is a matter of truth-preservation over cases, they say:
the conclusion should be true in every case in which the premises are
true. Each logic specifies a class of cases, but differs over which cases
should be considered. I show that this account of logic is incoherent.
Validity indeed is truth-preservation, provided this is properly understood. Once understood, there is one true logic, relevance logic. The
source of Beall and Restall’s error is a recent habit of using a classical metalanguage to analyse non-classical logics generally, including
relevance logic.