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Twenty four hundred years ago, Plato, one of history’s most famous thinkers, said life is like being chained up in a cave forced to watch shadows flitting across a stone wall. Beyond sounding quite morbid, what exactly did he mean? Alex Gendler unravels Plato's Allegory of the Cave, found in Book VII of "The Republic."

Lesson by Alex Gendler, animation by Stretch Films, Inc.