How do you know if something is true? And once you get there, how do you convince others? For over two thousand years, scientific progress has relied on different methods of establishing fact from fiction. From the medieval Islamic world to the recent pandemic, the reasoning went: achieve logical perfection, and you would be rewarded with ultimate, universal truth. But there is far more to proof than axioms, theories and laws: when demonstrating that a new medical treatment works, persuading a jury of someone's guilt, or deciding whether you trust a self-driving car or a financial transaction, the weighing up of evidence is far from simple. Bestselling author, statistician and epidemiologist Adam Kucharski ranges across science, politics, philosophy and economics, to explore how truth emerges - and why it falters.