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.Deductionargues that their logical competence depends, not 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 searching for alternative models that might refute the conclusion. The theory also resolves long-standing puzzles about reasoning, including how nonmonotonic reasoning occurs in daily life. The book reports experiments on all the main domains of deduction, including inferences based on prepositional connectives such as “if” and “or,” inferences based on relations such as “in the same place as,” inferences based on quantifiers such as “none,” “any,” and “only,” and metalogical inferences 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 model theory: inferences requiring only one model are easier than those requiring multiple models, and erroneous conclusions are usually the result of constructing only one of the possible models of the premises. (shrink)

Barry Barnes and David Bloor of the Strong Programme of the sociology of knowledge advance a naturalized epistemology that reduces all accounts of normativity to social causes. I endorse their program of naturalizing one kind of normativity, but I argue that there is another kind they cannot naturalize. Within the context of sociological explanations of rationality, there are norms of rationality instantiated by scientists that Barnes and Bloor study, and Barnes and Bloor's own normative ascriptions of scientists as rational beings. (...) I argue that Barnes and Bloor successfully justify their naturalization of the norms of rationality of the scientists they describe by a methodological caution and arguments from under-determination and finitism. But they inevitably fail to naturalize their own normative ascriptions of those scientists as rational. (shrink)