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Hardcover | Out of Print | 463 pp. | 6.2 x 9.1 in | March 1994 | ISBN: 9780262181532
Paperback | $40.00 X | £32.95 | 463 pp. | 6.2 x 9.1 in | December 2002 | ISBN: 9780262517218

The Psychology of Proof

Deductive Reasoning in Human Thinking


In this provocative book, Lance Rips describes a unified theory of natural deductive reasoning and fashions a working model of deduction, with strong experimental support, that is capable of playing a central role in mental life.

Rips argues that certain inference principles are so central to our notion of intelligence and rationality that they deserve serious psychological investigation to determine their role in individuals' beliefs and conjectures. Asserting that cognitive scientists should consider deductive reasoning as a basis for thinking, Rips develops a theory of natural reasoning abilities and shows how it predicts mental successes and failures in a range of cognitive tasks.

In parts I and II of the book, Rips builds insights from cognitive psychology, logic, and artificial intelligence into a unified theoretical structure. He defends the idea that deduction depends on the ability to construct mental proofs—actual memory units that link given information to conclusions it warrants. From this base Rips develops a computational model of deduction based on two cognitive skills: the ability to make suppositions or assumptions and the ability to posit sub-goals for conclusions. A wide variety of original experiments support this model, including studies of human subjects evaluating logical arguments as well as following and remembering proofs. Unlike previous theories of mental proof, this one handles names and variables in a general way. This capability enables deduction to play a crucial role in other thought processes,such as classifying and problem solving.

In part III, Rips compares the theory to earlier approaches in psychology which confined the study of deduction to a small group of tasks, and examines whether the theory is too rational or too irrational in its mode of thought.

About the Author

Lance J. Rips is Professor of Psychology at Northwestern University.


“Lance Rips writes with great simplicity and clarity about complicated matters. His judgment of issues is always fair and balanced. He is particularly fair to people with whom he disagrees, notably Harman and Johnson-Laird. The book constitutes a reasoned defense of natural logic. It argues that the mind is not a logical mess with, miraculously, a few logical pockets. It shows the central role of reasoning in all aspects of cognition and presents the case that the mind’s natural deductive systems are sound.”
John Macnamara, Professor of Psychology, McGill University
“This is a gem of a book. In it, Rips has provided a thorough and thoughtful analysis of human deductive reasoning and its relation to natural logics, nonmonotonic reasoning, and defeasible reasoning. In fact, his presentations of these topics make concise and clear introductions for readers who may not be familiar with the philosophical and AI literatures on reasoning. In its thoroughness and completeness, Rips’s theory can serve as a standard by which other researchers’ theory development and presentation are measured.”
Denise Dellarosa Cummins, University of Arizona
“This is one of the most important books to appear in the field of cognitive science in the last decade. More than any other contribution in the history of the field, it makes the case for the necessity, centrality, and generality of rule-based reasoning processes in cognition. Anyone interested in the nature of the human cognitive architecture should study this book. It is also a triumph of scholarship and literary style.”
Reid Hastie, Professor of Psychology, University of Colorado
“Lance Rips has written a tightly reasoned argument for the importance of deduction in human reasoning. This is exemplary cognitive science research, bringing together an incisive analysis of the literature in psychology, logic, and artificial intelligence with a computer model that embodies his theory of human deductive reasoning.”
Allan Collins, Principal Scientist, Bolt Beranek and Newman, Inc.