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Fallacies of Ambiguity

Various logical errors can arise because a term or statement is ambiguous and can be interpreted in more than one way.

For example Open in Syllogism-Finder App:

Nothing light can ever be dark.
All feathers are light.
Therefore, no feather can be dark.

Obviously, the term “light” is used in two different meanings here (equi­vocation): it is used to mean the opposite of “dark” in the major premise, but the opposite of “heavy” in the minor. This syllogism specifically commits the fallacy of the ambiguous middle term.

Other names

  • Ambiguity fallacy


The best-known and probably also most frequent forms of the ambiguity fallacy are based on equi­vocation – as in the example above, which is also a good example of a specific formal error in syllogisms known as the “four-term fallacy”.

However, ambiguity is not always as easy to recognize as in this example. Especially in the case of rather abstract terms, these can remain undetected and lead to equally subtle and difficult-to-recognise errors.

But not only the terms that are used in a statement can be ambiguous, ambiguity can also arise from the structure of a statement. This is described in the article on syntactic ambiguity.

In most situations, ambiguity concerns the extensions of the terms: that is, the objects that they refer to. But also the intensions of terms, i.e. the way that a statement refers to the object, can be the source of ambiguity. Such ambiguities can lead to intensional fallacies.

In this section

See also

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