MENTAL MODELS - THE REVISED THEORY BRINGS NEW PROBLEMS - COMMENTARY

How do people make deductions? The orthodox view in psychology is that they use formal rules of inference like those of a ''natural deductio n'' system. Deduction argues that their logical competence depends, no t on formal rules, but on mental models. they construct models of the situation described by the premises, using their linguistic knowledge and their general knowledge. They try to formulate a conclusion based on these models that maintains semantic information, that expresses it parsimoniously, and that makes explicit something not directly stated by any premise. They then test the validity of the conclusion by sear ching for alternative models that might refute the conclusion. the the ory also resolves long-standing puzzles about reasoning, including how nonmonotonic reasoning occurs in daily life. The book reports experim ents on all the main domains of deduction, including inferences based on propositional connectives such as ''if'' and ''or,'' inferences bas ed on relations such as ''in the same place as,'' inferences based on quantifiers such as ''none,'' ''any,'' and ''only,'' and metalogical i nferences based on assertions about the true and the false. Where the two theories make 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 requiring multiple models, and erroneous conclusions are usually the r esult of constructing only one of the possible models of the premises.