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Grandfather Paradox: If you use a time machine to stop your grandparents from meeting, you might prevent your own birth. But if you were never born, how could you have used the time machine in the first place?
Achilles and the Tortoise: Achilles, a fast runner, gives a tortoise a head start in a race. The paradox says Achilles will never pass the tortoise, because every time Achilles reaches where the tortoise was, the tortoise has moved a little. It keeps going like this forever, making it seem like Achilles can’t catch up.
Ship of Theseus: You have a ship and you replace all its parts. Is it still the same ship? If you use the old parts to build another ship, which one is the original?
Sorites Paradox: You have a heap of sand. If you remove one grain at a time, when does it stop being a heap?
Barber Shop Paradox: In a town, the rule is the barber shaves those who don’t shave themselves. But who shaves the barber? If he shaves himself, it breaks the rule. If he doesn’t, he should be shaved according to the rule.
Catch-22 Paradox: Needing something you can only have if you don’t need it. For example, a pilot can avoid dangerous flights if he’s insane, but asking not to fly shows he’s sane.
