Equivocation is classified as both a formal and informal fallacy. It is the misleading use of a term with more than one meaning (by glossing over which meaning is intended at a particular time).

It is often confused with amphiboly; however, equivocation is ambiguity arising from the misleading use of a word and amphiboly is ambiguity arising from misleading use of punctuation or syntax.

Examples

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:

A feather is light.

What is light cannot be dark.

Therefore, a feather cannot be dark.

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 is not true that all feathers are "bright"), equivocation is actually a kind 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 as they go in such a way to achieve equivocation by treating distinct meanings of the word as equivalent.

In English language, one equivocation is with the word "man", which can mean both "member of species Homo sapiens" and "male member of species Homo sapiens". A well-known equivocation is

"Do women need to worry about man-eating sharks?"

where "man-eating" is taken as "devouring only male human beings".

A separate case of equivocation is metaphor:

All Jackasses have long ears

Karl is a jackass

Therefore, Karl has long ears

Here the equivocation is the metaphorical use of "jackass" to imply a stupid or obnoxious person instead of a male ass.

Margarine is better than nothing

Nothing is better than butter

Therefore margarine is better than butter

In the first statement, "nothing" really means "dry bread" (such that the sentence means "it is preferable to have margarine [on bread] than nothing at all"), whereas in the second, it means, literally, "no thing" (so the sentence means "there exists no thing that is better than butter").

Specific types of equivocation fallacies

See main articles: False attribution, Fallacy of quoting out of context, Loki's Wager, No true Scotsman, Shifting ground fallacy.

References

• F.L. Huntley. "Some Notes on Equivocation: Comment", PMLA: Publications of the Modern Language Association of America Vol. 81, No 1, (March 1966), p.146.

• A.E. Malloch. "Some Notes on Equivocation", PMLA: Publications of the Modern Language Association of America Vol. 81, No 1, (March 1966), pp 145–146.

See also