Syntactic ambiguity

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For philosophical considerations of ambiguity, see ambiguity.

Syntactic ambiguity is a property of sentences which may be reasonably interpreted in more that one way, or reasonably interpreted to mean more than one thing. Ambiguity may or may not involve one word having two parts of speech or homonyms.

Syntactic ambiguity arises not from the range of meanings of single words, but from the relationship between the words and clauses of a sentence, and the sentence structure implied thereby. When a reader can reasonably interpret the same sentence as having more than one possible structure, the text is equivocal and meets the definition of syntactic ambiguity.

[edit] Contrast

Syntactic ambiguity can be contrasted with semantic ambiguity. The former represents multiple ways to infer the underlying structure of an entire sentence. The latter represents multiple ways to define individual words within a sentence (Layman E. Allen "Some Uses of Symbolic Logic in Law Practice" 1962J M.U.L.L. 119, at 120; and L.E. Allen & M.E. Caldwell "Modern Logic and Judicial Decision Making: A Sketch of One View" in H.W. Baade (ed.) "Jurimetrics" Basic Books Inc., New York, USA, 1963, 213, at 228).

[edit] Examples

Here are some examples:

Bear left at zoo. (Do you turn left when you get to the zoo, or did someone leave a bear there?)

I'm going to sleep. ("Going" can be a verb with destination "sleep" or an auxiliary indicating near future. There is little difference in meaning between the two parses.)

The word of the Lord came to Zechariah, son of Berekiah, son of Iddo, the prophet. (Which of the three is the prophet?)

British Left Waffles on Falklands (Did the British leave waffles behind, or was there waffling by the British Left?)

The cow was found by a stream by a farmer. (Did the farmer find the cow near the stream? Or was the cow found near a stream that was near a farmer?)

Monty flies back to front. (Monty returns to the frontline; or Monty flies backwards?)

Flying planes can be dangerous. (Either flying planes is dangerous, or flying planes are dangerous.)

(The following two are actually examples of scope ambiguities -- which operator is logically 'above' the other. Some linguistic theories consider them syntactic ambiguities, while other linguistics theories consider them semantic ambiguities.)

Someone ate every tomato. (Either some one person ate all of the tomatoes, or for each tomato there is some one person who ate it--Sally ate one, John at one, etc.)

Sally can not go to the movies. (Either Sally can't go to the movies, or she is simply capable of not going to the movies.)

A surgeon general's warning on packs of cigarettes in the United States reads, "Quitting smoking now greatly reduces your risk of cancer." (Quitting smoking today will reduce your risk of cancer; As opposed to the past, quitting smoking today reduces the chance of cancer)

A noteworthy example in the field of computer natural language processing is Time flies like an arrow. Although humans unambiguously understand it to mean "Time flies in the same way that an arrow does," it could also mean:

"Measure the speed of flies as you would for an arrow,"
"Measure the speed of those flies that are similar to an arrow,"
"Measure the speed of flies as an arrow would," or even
"A kind of fly, the time fly, likes arrows."

(As Groucho Marx is said to have observed, "Time flies like an arrow; fruit flies like a banana.")

In legal disputes, courts may be asked to interpret the meaning of syntactic ambiguities in statutes or contracts. In some instances, arguments asserting highly unlikely interpretations have been deemed frivolous.