In this book, Keith Stanovich attempts to resolve the Great Rationality Debate in cognitive science - the debate about how much irrationality to ascribe to human cognition. Stanovich shows how the insights of dual-process theory and evolutionary psychology can be combined to explain why humans are sometimes irrational even though they possess cognitive machinery of remarkable adaptiveness. Using a unique individual differences approach, Stanovich shows that to fully characterize differences in rational thinking, the traditional System 2 of dual-process theory must be partitioned into the reflective mind and the algorithmic mind. He posits that we need to supersede dual-process theories with tripartite models of cognition. The key operations of the algorithmic mind and the reflective mind that support human rationality are discussed in the book. The key function of the algorithmic mind is to sustain the processing of decoupled secondary representations in cognitive simulation. The key function of the reflective mind, in contrast, is to detect the need to interrupt autonomous processing and to begin simulation activities. Stanovich uses the algorithmic/reflective distinction to develop a taxonomy of cognitive errors that are made on tasks in the heuristics and biases literature. He presents empirical data to show that the tendency to make these thinking errors is only modestly related to intelligence. Using the new tripartite model of mind, Stanovich shows how rationality is a more encompassing construct than intelligence - when both are properly defined - and that IQ tests fail to assess individual differences in rational thought. Stanovich discusses the types of thinking processes that would be measured in an assessment of rational thinking.