Father or son? Mother or daughter?


Taxonomy: Logical Fallacy > Informal Fallacy > Ambiguity


I did not have sexual relations with that woman, Miss Lewinsky.

Analysis of the Example


As a feature of language, ambiguity occurs when a word or phrase has more than one meaning. For instance, the word "note" can mean either:

  1. A musical tone.
  2. A short written record.

In fact, the Random House College Dictionary lists twenty meanings of "note", though one of these is archaic. Even the part of speech is ambiguous, since "note" can be either a noun or verb. This situation is not at all unusual, and "note" is not a especially ambiguous word. Opening any dictionary at random will confirm that it is the rare word that is not ambiguous. In fact, ambiguity tends to increase with frequency of use, and it is rarely-used technical terms that are unambiguous. For instance, "is" is highly ambiguous and has, as a result, caused much mischief in metaphysics, and even politics.

As a logical fallacy, ambiguity occurs when linguistic ambiguity causes an argument to appear cogent when it is not. This can happen when an ambiguous word or phrase occurs more than once in an argument and has different meanings in two or more occurrences.

There are two main types of ambiguity:

  1. Lexical: A word or short phrase that is ambiguous. As noted above, "note" is lexically ambiguous. When an argument commits a fallacy based on lexical ambiguity, it is called "equivocation"―see the subfallacy, below.
  2. Structural: A phrase, sentence, or passage that is grammatically ambiguous. For instance, the phrase "ancient philosophy professor" can either mean a teacher of Greek and Roman philosophy, or a very old professor of philosophy. An argument that commits a fallacy based on structural ambiguity is said to be "amphibolous"― again, see the subfallacy, below.


Because of the ubiquity of ambiguity in natural language, it is important to realize that its presence in an argument is not sufficient to render it fallacious, otherwise, all such arguments would be fallacious. Most ambiguity is logically harmless, a fallacy occurring only when ambiguity causes an argument to appear cogent when it is not. While not always a fallacy, ambiguity can be misleading and is sometimes a logical boobytrap―as in the Example, above, see the Analysis―that is, it may cause someone to inadvertently commit a fallacy.

Funny Fallacy:

Unintentionally ambiguous statements are frequently sources of humor, especially when one of the possible meanings is ludicrous. For example:

Police blotter

Sent city police out at 11:38 a.m. to kick kids off the roof of a downtown furniture store.

Source: Jay Leno (compiler), More Headlines: Real but Ridiculous Samplings from America's Newspapers (Warner Books, 1990), p. 8.


Analysis of the Example:

The example, of course, is the much publicized statement by President Clinton. This was testimony, rather than argument, so it cannot be fallacious. However, it is now clear that it was intended to snare the listener into concluding, falsely, that there was no sexual relationship between the President and Miss Lewinsky. In other words, Clinton's words were a logical boobytrap. The ambiguity came from the phrase "sexual relations", which has a broad and narrow meaning:

  1. A sexual relationship
  2. Sexual intercourse

As he later admitted, President Clinton had had "sexual relations" with Miss Lewinsky in the broad sense (1), and he was denying it only in the narrow sense (2).