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In logic, equivocation ('calling two different things by the same name') is an informal fallacy resulting from the use of a particular word/expression in multiple senses throughout an argument leading to a false conclusion.[1][2] Abbott and Costello's "Who's on first?" routine is a well known example of equivocation.[3][4]

It is a type of ambiguity that stems from a phrase having two distinct meanings, not from the grammar or structure of the sentence.[1]

Some examples of equivocation in syllogisms (a logical chain of reasoning) are below:

  • Since only man [human] is rational,
and no woman is a man [male],
Therefore, no woman is rational.[1]
  • A feather is light [not heavy].
What is light [bright] cannot be dark.
Therefore, a feather cannot be dark.

In the above example, distinct meanings of the word "light" are implied in contexts of the first and second statements.

  • All jackasses have long ears.
Carl is a jackass.
Therefore, Carl has long ears.

Here, the equivocation is the metaphorical use of "jackass" to imply a simple-minded or obnoxious person instead of a male donkey.

See also[edit]


  1. ^ a b c Damer, T. Edward (21 February 2008). Attacking Faulty Reasoning: A Practical Guide to Fallacy-Free Arguments. Cengage Learning. pp. 121–123. ISBN 0-495-09506-0.
  2. ^ Fischer, D. H. (June 1970), Historians' fallacies: toward a logic of historical thought, Harper torchbooks (first ed.), New York: HarperCollins, p. 274, ISBN 978-0-06-131545-9, OCLC 185446787
  3. ^ Curtis, Gary (n.d.). "Logical Fallacy: Equivocation". The Fallacy Files. Retrieved 17 July 2017.
  4. ^ Abbott & Costello Who's On First on YouTube