From the reviews: "Rigid Flexibility presents a new theory of cognition. As such it is devoted to the general research for Artificial Intelligence (AI), in contrast to a focus of other AI research that is focusing on solving specific reasoning problems such as planning or learning for example. ... The review of the principles and assumptions underlying the various streams of AI research make this book very interesting to read and enable the reader to easily compare the presented theory with other existing approaches." (Jana Koehler, Zentralblatt MATH, Vol. 1122 (24), 2007)

• Theoretical Foundation.- The Goal of Artificial Intelligence.- A New Approach Toward AI.- Non-Axiomatic Reasoning System.- The Core Logic.- First-Order Inference.- Higher-Order Inference.- Inference Control.- Comparison and Discussion.- Semantics.- Uncertainty.- Inference Rules.- NAL as a Logic.- Categorization and Learning.- Control and Computation.- Conclusions.- Current Results.- NARS in the Future.