PRECIS OF DEDUCTION

How do people make deductions? The orthodox view in psychology is that they use formal rules of inference like those of a natural deduction' ' system. Deduction argues that their logical competence depends, not on formal rules, but on mental models. They construct models of the si tuation described by the premises, using their linguistic knowledge an d their general knowledge. They try to formulate a conclusion based on these models that maintains semantic information, that expresses it p arsimoniously, and that makes explicit something not directly stated b y any premise. They then test the validity of the conclusion by search ing for alternative models that might refute the conclusion. The theor y also resolves long-standing puzzles about reasoning, including how n onmonotonic reasoning occurs in daily life. The book reports experimen ts on all the main domains of deduction, including inferences based on propositional connectives such as ''if'' and ''or,'' inferences based on relations such as ''in the same place as,'' inferences based on qu antifiers such as ''none,'' ''any,'' and ''only,'' and metalogical inf erences based on assertions about the true and the false. Where the tw o theories intake opposite predictions, the results confirm the model theory and run counter to the formal rule theories. Without exception, all of the experiments corroborate the two main predictions of the mo del theory inferences requiring only one model are easier than those r equiring multiple models, and erroneous conclusions are usually the re sult of constructing only one of the possible models of the premises.