A THEORY OF IF - A LEXICAL ENTRY, REASONING PROGRAM, AND PRAGMATIC PRINCIPLES

The theory has 3 parts: (a) A lexical entry defines the information about if in semantic memory; its core comprises 2 inference schemas, Modus Ponens and a schema for Conditional Proof; the latter operates under a constraint that explains differences between if and the material conditional of standard logic. (b) A propositional-logic reasoning program specifies a routine for reasoning from information as interpreted to a conclusion. (c) A set of pragmatic principles governs how an if sentence is likely to be interpreted in context. The reasoning program and the pragmatic principles are independently motivated. The theory accounts well for relevant research data-explaining inferences, fallacies, truth judgments, and comprehension errors-and both schemas appear to be available early to children. Other psychological theories are incomplete. Stainaker's philosophical theory is more complex and begs questions about how possible worlds are apprehended.