 non-well-founded set theory: Encyclopedia - Circular definitionA circular definition is one that assumes a prior understanding of the term being defined. For instance, we can define "oak" as a tree which has catkins and grows from an acorn, and then define "acorn" as the nut produced by an oak tree. To someone not knowing either which trees are oaks or which nuts are acorns, the definition is fairly useless.
A circular definition occurred in an early definition of the kilogram. The kilogram was originally defined as the mass of one litre of water at standard pressure and the temperature at ...
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