ABSTRACT
As part of an ongoing debate between advocates of the mental-logic and mentalmodels theories, Byrne (1989, 1991) claimed that modus-ponens inferences (i.e., of the form If P then Q, P, therefore Q) can be suppressed, and that this demonstrates that the mind does not have a schema for modus ponens. Given that mental-logic theory includes modus ponens among its basic inferences, Byrne’s claim, if correct, would present a serious challenge. We show here, however, that the data presented by Byrne are consistent with the predictions of mental-logic theory and thus present no challenge. The reason that Byrne’s data do not challenge mental-logic theory is that the sorts of problems she presented that putatively led to suppression of modus ponens violated one of the conditions for making an inference: For a reasoner to apply a schema, its premises must be assumed true (see discussion of the soundness of the schemas in chap. 3), and this condition is violated in the problems reported by Byrne (1989), as we show later.
