In philosophy and logic, the property of having the same scope or applying to the same set of things; the state of extending equally.
From co- 'together' + extension (Latin extendere: ex- 'out' + tendere 'to stretch'). A philosophical term developed to describe equivalent logical or semantic reach.
Philosophers argue that 'bachelor' and 'unmarried man' have coextension—they apply to exactly the same people—but they don't have the same meaning, which reveals something deep about how language works.
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