Equivocation Fallacy
Also known as: Equivocation, Fallacy of Ambiguity, Semantic Shift
Formulated by Aristotle (-350)
Definition
A logical fallacy in which a single word or phrase is used with two different meanings at different points in an argument, so that the conclusion appears to follow only because the ambiguity is never resolved. The argument looks valid on its surface because the same term keeps reappearing, but the term has quietly changed meaning underneath the words. Aristotle catalogued equivocation among the fallacies 'dependent on language' in his Sophistical Refutations, alongside amphiboly and accent, as ways an argument can seem rigorous while resting on a linguistic trick rather than a real inference. A classic modern example is the word 'income': a report can state that a group paid a very low tax rate on its 'economic income' while including unrealized appreciation of assets in that figure, then let the reader silently substitute the everyday meaning of income, cash actually received, producing outrage that the underlying numbers never actually support.