From sex and music to religion and politics, a history of irrationality and the ways in which it has always been with us — and always will be. In this sweeping account of irrationality from antiquity to the rise of Twitter mobs and the election of Donald Trump, Justin Smith argues that irrationality makes up the greater part of human life and history. Ranging across philosophy, politics, and current events, he shows that, throughout history, every triumph of reason has been temporary and reversible, and that rational schemes often result in their polar opposite. Illuminating unreason at a moment when the world appears to have gone mad again, Irrationality is timely, provocative, and fascinating. 'Stippled with fascinating meditations and vignettes.' — Kwame Anthony Appiah, New York Review of Books 'Irrationality is unique among recent paeans to Enlightenment and liberalism in marrying a resolute defence of reason with a recognition of how futile such defences tend to be.' — William Davies, London Review of Books 'No philosopher alive today writes with as much wit, voice, and erudition as Justin Smith. Irrationality is a masterpiece: an urgent warning that no grand design of perfect rationality can provide the solution to the depravity of this political moment.' — Yascha Mounk, author of The People vs. Democracy 'A learned, ludic, and often profound meditation on how the perverse dialectic of reason and unreason has played out over history.' — Jim Holt, author of Why Does the World Exist?