If reason is what makes us human, then why do we humans often behave so irrationally? Taking us from desert ants to Aristotle, cognitive psychologists Hugo Mercier and Dan Sperber explore how our 'flawed superpower' of reason works, how it doesn't, and how it evolved to help us develop as social beings. 'Original and provocative ... likely to have a big impact on our understanding of ourselves' Steven Pinker 'Brilliant, elegant and compelling ... turns reason's weaknesses into strengths, arguing that its supposed flaws are actually design features that work remarkably well ... A timely and necessary book' Julian Baggini, Financial Times 'Hugo Mercier and Dan Sperber have solved one of the most important and longstanding puzzles in psychology' Jonathan Haidt 'Reason is more likely to confirm things that we want to be true, or which we already believe. So why does it exist? This book provides the answer' Alex Dean, Prospect