Abstract

This chapter argues that people aim to make rational deductions – to infer conclusions that have no counterexamples. Logic might therefore seem to be their ultimate guide. But, that cannot be. Orthodox logic has intrinsic bounds, and it allows irrational inferences, such as the conjunction of a premise with itself. It also tolerates contradictions, implying that any conclusion whatsoever follows from them. People are more rational. They don’t draw the silly conclusions. And when facts are in blatant contradiction with a conclusion, they withdraw it, and seek an explanation that resolves the conflict. The chapter therefore presents an alternative account of rational deductions based on the theory that people depend on the construction of mental models of possibilities. These possibilities and the conclusions they imply are tentative, and people withdraw them when they realize that they conflict with the facts. Their knowledge alters their interpretation of terms such as “if”, which are constants in logic. But, their reasoning is usually intuitive and based on simple mental models, which can lead them into systematic and compelling fallacies. They can correct these errors if they deliberate and construct models that make explicit each possibility consistent with the premises. In sum, rational deductions depend on mental simulations of the world, some of which unfold in time akin to the events they represent. The chapter describes crucial experiments that corroborate this account.