In this provocative book, Lance Rips describes a unified theory ofnatural deductive reasoning and fashions a working model of deduction, with strongexperimental support, that is capable of playing a central role in mental life.Ripsargues that certain inference principles are so central to our notion ofintelligence and rationality that they deserve serious psychological investigationto determine their role in individuals’ beliefs and conjectures. Asserting thatcognitive scientists should consider deductive reasoning as a basis for thinking, Rips develops a theory of natural reasoning abilities and shows how it predictsmental successes and failures in a range of cognitive tasks.In parts I and II of thebook Rips builds insights from cognitive psychology, logic, and artificialintelligence into a unified theoretical structure. He defends the idea thatdeduction depends on the ability to construct mental proofs - actual memory unitsthat link given information to conclusions it warrants. From this base Rips developsa computational model of deduction based on two cognitive skills: the ability tomake suppositions or assumptions and the ability to posit sub-goals for conclusions.A wide variety of original experiments support this model, including studies ofhuman subjects evaluating logical arguments as well as following and rememberingproofs. Unlike previous theories of mental proof, this one handles names andvariables in a general way. This capability enables deduction to play a crucial rolein other thought processes, such as classifying and problem solving.In part III Ripscompares the theory to earlier approaches in psychology which confined the study ofdeduction to a small group of tasks, and examines whether the theory is too rationalor too irrational in its mode of thought.Lance J. Rips is Professor of Psychology atNorthwestern University.
