Knowing what separates wakeful reality from dream states seems rather simple on its surface. After all, even if a dream feels quite real in the moment, it’s unbound from continuity and the natural laws of our (presumed) waking lives. Yet proving that you’re awake, rather than just intuiting it, has been a perilous task for philosophers across the centuries. Beginning with the ancient Chinese philosopher Zhuang Zhou’s famed butterfly dream, this TED-Ed animation tackles how thinkers from Al-Ghazali in medieval Persia, to René Descartes and Thomas Hobbes in 17th-century France and England, to neuroscientists today have approached the question of whether we can ever truly know we’re awake.
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Future of technology
Artificial ‘creativity’ is unstoppable. Grappling with its ethics is up to us
23 minutes
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Thinkers and theories
Jeremy Bentham was consumed by creating a perfect prison. Here’s the result
4 minutes
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Logic and probability
Chew over the prisoner’s dilemma and see if you can find the rational path out
6 minutes
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Architecture
The radically impractical 18th-century architect whose ideas on beauty endure
19 minutes
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Metaphysics
Bertrand Russell wanted to kill off causation. Can contemporary philosophy rescue it?
8 minutes
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Ethics
How many monkeys is it worth sacrificing to save a human life?
6 minutes
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Human rights and justice
Thirty years after one teenager shot another, is it time to forgive?
28 minutes
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Chemistry
A square inch in a Petri dish becomes a grand stage for chemical transformations
4 minutes
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Virtues and vices
From violent criminal to loving parent – a son’s story of his father’s transformation
23 minutes