Equivocation is classified as both a formal and informal logical fallacy. It is the misleading use of a term with more than one meaning or sense (by glossing over which meaning is intended at a particular time). It generally occurs with polysemic words.
It is often confused with amphibology (amphiboly); however, equivocation is ambiguity arising from the misleading use of a word and amphiboly is ambiguity arising from the misleading use of punctuation or syntax.
This form of word play relies upon two different words that sound alike. However, their different senses become obvious only upon a moment's reflection. One example is the contrast between birth and death, and birth and berth, and told and toll'd in Thomas Hood's account of the death of Ben the sailor (which took place at the age of 40, contrasted with his age of zero at birth) in his humorous poem Faithless Sally Brown:
Equivocation is the use in a syllogism (a logical chain of reasoning) of a term several times, but giving the term a different meaning each time. For example:
In this use of equivocation, the word "light" is first used as the opposite of "heavy", but then used as a synonym of "bright" (the fallacy usually becomes obvious as soon as one tries to translate this argument into another language). Because the "middle term" of this syllogism is not one term, but two separate ones masquerading as one (all feathers are indeed "not heavy", but it is not true that all feathers are "bright"), this type of equivocation is actually an example of the fallacy of four terms.
The fallacy of equivocation is often used with words that have a strong emotional content and many meanings. These meanings often coincide within proper context, but the fallacious arguer does a semantic shift, slowly changing the context by treating, as equivalent, distinct meanings of the term.
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