A clear, concise and fascinating guide to philosophical thought experiments and how they've shaped our understanding of the world. From Plato's Cave to Descartes' Demon, great thinkers have used thought experiments and paradoxes to try and work out complex ideas in the simplest way possible. Among the most famous thought experiments is Zeno's Achilles and the Tortoise: if Achilles is faster than the tortoise, why will Achilles never catch up with the tortoise when it starts ahead of him? Zeno proposes that, when Achilles reaches the point where the tortoise started the race, the tortoise will have already moved on. And as Achilles runs on to where the tortoise was last, when he reaches that point the tortoise has moved again. Therefore poor Achilles will never catch up with the tortoise as the distance he must run gets smaller and smaller and each time he has less and less time to run. Starting in Ancient Greece, Joel Levy guides us through the mind-bending world of thought experiments and their role in revealing the complexity of morality, exploring the limitations and the infinite possibilities of the human mind.