Constituent as used in syntactic analysis refers to a word or a group of words that function together as a unit and are embedded into a hierarchical structure. Syntax, originating from the Greek words συν (syn, meaning co- or together) and τάξις (táxis, meaning sequence, order, arrangement), can in linguistics be described as the study of the rules, or patterned relations that govern the way the words in a sentence come together. ...

Phrases (noun phrases, verbal phrases, etc.) are usually constituents of a clause, but clauses may also be embedded into a bigger structure. For example, in the phrase "I didn't hear what you said," the subordinate clause "what you said" is embedded into the main clause and is syntactically its object; this can be demonstrated by substituting the pronoun "it" for the subordinate clause "I didn't hear it." A phrase is a group of words that functions as a single unit in the syntax of a sentence. ... In grammar, a clause is a group of words consisting of a subject and a predicate, although, in non-finite clauses, the subject is often not explicitly given. ... A clause is a group of words consisting of a subject (often just a single noun) and a predicate (sometimes just a single verb). ... In linguistics and grammar, a pronoun is a pro-form that substitutes for a noun phrase. ...

Constituency tests

Various constituency tests exist. Some syntacticians assert it is sufficient to pass only a single test for a sequence of words to be a constituent^{[citation needed]}; others arrange such tests on a scale of reliability, with less-reliable tests treated as useful to confirm constituency though not sufficient on their own^[1].

Failing to pass a test, however, does not always mean that the unit is not a constituent. It is best to apply as many tests as possible to a given unit in order to prove or to rule out its constituency.

Substitution (replacement)

Using "it" instead of the whole clause "what you said" is called substitution, or replacement. This is one of the tests used to determine the internal structure of a sentence, i.e. to determine its constituents. Substitution normally involves using pronouns like it, he, there, here etc. in place of a phrase or a clause. If such a change yields a grammatical sentence where the general structure has not been altered, then the sequence of words which is being tested is a constituent: In linguistics, a sentence is a unit of language, characterised in most languages by the presence of a finite verb. ...

e.g. I don't know this young man in a long coat.

I don't know him in a long coat. (ungrammatical)

I don't know him.

The ungrammaticality of the first changed version and the grammaticality of the second one demonstrates that the whole sequence, this young man in a long coat, and not just this young man is a constituent functioning as a unit.

Movement

Movement includes such operations as clefting, fronting, pseudo-clefting and passivization.

Fronting is the simplest movement operation when the sequence we want to test is moved to the front of the sentence:

He is going to attend another language course to improve his English.

To improve his English, he is going to attend another course.

Clefting involves placing a sequence of words X within the structure beginning with "It is/was": It was X that...

She bought a pair of gloves with silk embroidery.

It was a pair of gloves with silk embroidery that she bought.

Pseudo-clefting (also preposing) is similar to clefting in that it puts emphasis on a certain phrase in a sentence. It involves inserting a sequence of words before "is/are what" or "is/are who":

A pair of gloves with silk embroidery is what she bought.

Passivization involves more than just movement. Apart from putting the object in the subject position and the subject after the preposition by, it also triggers changes in the verb form: An object in grammar is a sentence element and part of the sentence predicate. ... The subject of a sentence is one of the two main parts of a sentence, the other being the predicate. ... It has been suggested that this article or section be merged with adposition. ... A verb is a part of speech that usually denotes action (bring, read), occurrence (decompose, glitter), or a state of being (exist, stand). Depending on the language, a verb may vary in form according to many factors, possibly including its tense, aspect, mood and voice. ...

A car driving at breakneck speed nearly hit the little dog.

The little dog was nearly hit by a car driving at breakneck speed.

In case passivization results in a grammatical sentence, the phrases that have been moved can be regarded as constituents.

The stand-alone test

This test refers to the ability of a sequence of words to stand alone as a reply to a question. It is often used to test the constituency of a verbal phrase but can also be applied to other phrases:

What did you do yesterday? - Worked on my new project.

vs.

What did you do yesterday? - Worked on. (ungrammatical, which means that [worked on] is not a unit).

Linguists do not agree whether passing the stand-alone test is sufficient, though at a minimum they agree that it can help confirm the results of another constituency test^[1].

Other tests

Other constituency tests can be used in a limited number of syntactic environments:

• Deletion checks whether a sequence of words can be omitted without influencing the grammaticality of the sentence — in most cases local or temporal adverbials can be safely omitted and thus constitute a syntactic unit;
• Coordination relies on the fact that only constituents can be coordinated, i.e., joined by means of the coordinating conjunction "and" (e.g., He enjoys [writing short stories] and [reading them to his friends].)

Constituency tests and disambiguation

Syntactic ambiguity characterizes sentences which can be intepreted in different ways depending solely on how one perceives syntactic connections between words and arranges them into phrases.

Possible interpretations of the sentence They killed the man with a gun: a) The man was shot;

b) the man who was killed had a gun with him.

The ambiguity of this sentence results from 2 possible arrangements into constituents:

a) [They] {killed [the man] [with a gun]}.

b) [They] {killed [the man with a gun]}.

In a) with a gun is an independent constituent with instrumental meaning , in b) it is embedded into the noun phrase the man with a gun modifying the noun man. The autonomy of the unit with a gun in the first interpretation can be tested by the Stand-Alone test: In linguistics, the instrumental case (also called the eighth case) indicates that a noun is the instrument or means by which the subject achieves or accomplishes an action. ...

How did they kill the man? - With a gun.

However, the same test can be used to prove that the man with a gun in b) should be treated as a unit:

Who(m) did they kill? - The man with a gun.

References

General references:

• Burton-Roberts, N. (1997) Analysing Sentences: An Introduction to English Syntax. 2nd Edition. Longman. pp. 7-23
• Carnie, A. (2002) Syntax: A Generative Introduction. Oxford: Blackwell. pp. 51-53

Specific references:

1. ^ ^a b April 22, 2006 Language Log posting by Eric Bakovic of University of California, San Diego