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A phrase often used by science deniers, usually against the scientific theory of evolution. It implies that a "theory" is just an unproven "guess", therefore evolution is an unproved lie. This stems from a fundamental misunderstanding of the word "theory" in the context of science. In colloquial use, a 'theory' may mean a "guess", but in Science, a 'theory' is defined as "a well-substantiated explanation of an aspect of the natural world." Therefore the phrase "Evolution is just a theory" makes no sense.
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