Syntactic Ambiguity

A joke using syntactic ambiguity
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In English grammar, syntactic ambiguity is the presence of two or more possible meanings within a single sentence or sequence of words. Also called structural ambiguity or grammatical ambiguity. Compare with lexical ambiguity (the presence of two or more possible meanings within a single word).

The intended meaning of a syntactically ambiguous sentence can often (but not always) be determined by context.

Examples and Observations

  • The professor said on Monday he would give an exam.
  • The chicken is ready to eat.
  • The burglar threatened the student with the knife.
  • Visiting relatives can be boring.
  • "This morning I shot an elephant in my pajamas. How he got in my pajamas I don't know."
    (Groucho Marx
  • "A lady with a clipboard stopped me in the street the other day. She said, 'Can you spare a few minutes for cancer research?' I said, 'All right, but we're not going to get much done.'"
    (English comedian Jimmy Carr
  • "'Planes can go around the world, iPhones can do a zillion things, but humans have not invented a machine that can debone a cow or a chicken as efficiently as a human being,' says Alan Alanis, a JPMorgan Chase (JPM) analyst."
    (Bryan Gruley and Lucia Kassai, "Brazilian Meatpacker JBS Wrangles the U.S. Beef Industry." Bloomberg Businessweek, September 19, 2013)

Types of Ambiguity

We can crudely classify the sorts of ambiguity found in sentences as follows:

1. Pure syntactic ambiguity:
old men and women
French silk underwear
2. Quasi-syntactic ambiguity:
The astronaut entered the atmosphere again.
a red pencil
3. Lexico-syntactic ambiguity:
We saw her duck.
I saw the door open.
4. Pure lexical ambiguity:
He reached the bank.
What is his position?

The statement 'pure syntactic ambiguity' is meant ambiguity in which the variant readings of a sentence involve identical lexical units; the ambiguity is thus necessarily a matter merely of the way the elements are grouped together."
(D. A. Cruse, Lexical Semantics. Cambridge University Press, 1986

Using Speech Cues to Decipher Syntactic Ambiguity
"Some sentences are syntactically ambiguous at the global level, in which case the whole sentence has two or more possible interpretations. For example, 'They are cooking apples' is ambiguous because it may or may not mean that apples are being cooked. . . .
"One of the ways in which listeners work out the syntactic or grammatical structure of spoken sentences is by using prosodic cues in the form of stress, intonation, and so on. For example, in the ambiguous sentence 'The old men and women sat on the bench,' the women may or may not be old. If the women are not old, then the spoken duration of word 'men' will be relatively long and the stressed syllable in 'women' will have a steep rise in speech contour. Neither of these prosodic features will be present if the sentence means the women are old."
(M. Eysenck and M. Keane, Cognitive Psychology. Taylor & Francis, 2005

Ambiguous Structures
"Syntactic ambiguity occurs when a sequence of words can be structured in alternative ways that are consistent with the syntax of the language. For instance, . . . [this word group] is ambiguous:

(1) a. John told the woman that Bill was dating. . . .

In 1a, "that Bill was dating" could either be a relative clause (as in 'John told the woman that Bill was dating a lie') or a sentence complement (as in 'John told the woman that Bill was dating a liar')."
(Patrizia Tabossi et al., "Semantic Effects on Syntactic Ambiguity Resolution" in Attention and Performance XV, ed. by C. Umiltà. MIT Press, 1994)