Steven Pinker's "Rationality" explores the nature of sound reasoning, investigating why it often seems scarce despite humanity's evident intelligence. The book examines the foundations of rationality through logic, critical thinking, probability, and rational choice theory, highlighting common cognitive biases and fallacies that lead to irrational behavior. Pinker also considers instances where apparent irrationality might serve underlying rational goals, touching upon topics like morality, self-control, and social dynamics. Ultimately, the work advocates for understanding and enhancing our rational capacities to improve individual lives and public policy.