Processing of logically valid and logically invalid conditional inferences in discourse comprehension.

Two competing theories of processing of conditionals (if-then) were tested. Syntactic theories posit that people only draw inferences conforming to the logically valid modus ponens (MP) schema. Mental models theories predict that people draw MP and invalid affirming-the-consequent (AC) inferences. Three experiments tested these predictions. Participants read short stories that conformed to either the MP or AC form but without conclusions, and they completed either priming or recognition tasks. Results indicate that both MP and AC inferences occur during discourse processing: MP and AC premise forms prime their respective conclusions, participants erroneously judged that they had read the conclusions to MP and AC arguments, and AC inferences did not stem from a biconditional interpretation of conditionals. Findings support mental models theories.