Do people solve inferential problems in everyday life by using abstract inferential rules or do they use only rules specific to the problem domain? The view that people possess abstract inferential rules and use them to solve even the most mundane problems can be traced back to Aristotle. In modern psychology, this view is associated with the theories of Piaget and Simon. They hold that, over the course of cognitive development, people acquire general and abstract rules and schemas for solving problems. For example, people acquire rules that correspond to the laws of formal logic and the formal rules of probability theory. Problems are solved by decomposing their features and relations into elements that are coded in such a way that they can make contact with these abstract rules.

This formalist view has been buffeted by findings showing that people violate the laws of formal logic and the rules of statistics. People make serious logical errors when reasoning about arbitrary symbols and relations (for a review, see Evans, 1982). The best known line of research is that initiated by Wason (1966) on his selection task. In that task, subjects are told that they will be shown cards having a letter on the front and a number on the back. They are then presented with cards having an A,a B,a 4, and a 7 and asked which they would have to turn over in order to verify the rule, “If a card has an A on one side, then it has a 4 on the other.”