In syntactic analysis, a constituent is a word or a group of words that function as a single unit within a hierarchical structure. The constituent structure of sentences is identified using tests for constituents.Osborne (2018) provides a detailed and comprehensive discussion of tests for constituents, having surveyed dozens of textbooks on the topic. Osborne's article is available here: Tests for constituents: What they really reveal about the nature of syntactic structure . See also Osborne (2019: 2–6, 73–94). These tests apply to a portion of a sentence, and the results provide evidence about the constituent structure of the sentence. Many constituents are phrases. A phrase is a sequence of one or more words (in some theories two or more) built around a head lexical item and working as a unit within a sentence. A word sequence is shown to be a phrase/constituent if it exhibits one or more of the behaviors discussed below. The analysis of constituent structure is associated mainly with phrase structure grammars, although dependency grammars also allow sentence structure to be broken down into constituent parts.
Tests for constituents in English Tests for constituents are diagnostics used to identify sentence structure. There are numerous tests for constituents that are commonly used to identify the constituents of English sentences. 15 of the most commonly used tests are listed next: 1) coordination (conjunction), 2) pro-form substitution (replacement), 3) topicalization (fronting), 4) do-so-substitution, 5) one-substitution, 6) answer ellipsis (question test), 7) clefting, 8) VP-ellipsis, 9) pseudoclefting, 10) passivization, 11) omission (deletion), 12) intrusion, 13) wh-fronting, 14) general substitution, 15) right node raising (RNR).
The order in which these 15 tests are listed here corresponds to the frequency of use, coordination being the most frequently used of the 15 tests and RNR being the least frequently used. A general word of caution is warranted when employing these tests, since they often deliver contradictory results. The tests are merely rough-and-ready tools that grammarians employ to reveal clues about syntactic structure. Some syntacticians even arrange the tests on a scale of reliability, with less-reliable tests treated as useful to confirm constituency though not sufficient on their own. Failing to pass a single test does not mean that the test string is not a constituent, and conversely, passing a single test does not necessarily mean the test string is a constituent. It is best to apply as many tests as possible to a given string in order to prove or to rule out its status as a constituent.
The 15 tests are introduced, discussed, and illustrated below mainly relying on the same one sentence:This one sentence has been adapted slightly from Radford 1988:91. Radford uses this sentence to introduce and illustrate sentence structure and tests for constituents that identify this structure.
Drunks could put off the customers.
By restricting the introduction and discussion of the tests for constituents below mainly to this one sentence, it becomes possible to compare the results of the tests. To aid the discussion and illustrations of the constituent structure of this sentence, the following two sentence diagrams are employed (D = determiner, N = noun, NP = noun phrase, Pa = particle, S = sentence, V = Verb, VP = verb phrase):
These diagrams show two potential analyses of the constituent structure of the sentence. A given node in a tree diagram is understood as marking a constituent, that is, a constituent is understood as corresponding to a given node and everything that that node exhaustively dominates. Hence the first tree, which shows the constituent structure according to dependency grammar, marks the following words and word combinations as constituents: Drunks, off, the, the customers, and put off the customers.Two prominent sources on dependency grammar are Tesnière (1959) and Ágel, et al. (2003/2006). The second tree, which shows the constituent structure according to phrase structure grammar, marks the following words and word combinations as constituents: Drunks, could, put, off, the, customers, the customers, put off the customers, and could put off the customers. The analyses in these two tree diagrams provide orientation for the discussion of tests for constituents that now follows.
Coordination The coordination test assumes that only constituents can be coordinated, i.e., joined by means of a coordinator such as and, or, or but.For examples of coordination used as a test for constituent structure, see Baker 1978:269–76; Radford 1981:59–60; Atkinson et al. 1982:172–3; Radford 1988:75–8; Akmajian et al. 1990:152–3; Borsley 1991:25–30; Cowper 1992:34–7; Napoli 1993:159–61; Ouhalla 1994:17; Radford 1997:104–7; Burton–Roberts 1997:66–70; Haegeman and Guéron 1999:27; Fromkin 2000:160–2; Lasnik 2000:11; Lobeck 2000:61–3; Börjars and Burridge 2001:27–31; Huddleston and Pullum 2002:1348–9; van Valin 2001:113–4; Poole 2002:31–2; Adger 2003:125–6; Sag et al. 2003:30; Radford 2004:70–1; Kroeger 2005:91, 218–9; Tallerman 2005:144–6; Haegeman 2006:89–92; Payne 2006:162; Kim and Sells 2008:22; Carnie 2010:115–6, 125; Quirk et al. 2010:46–7; Sobin 2011:31–2; Carnie 2013:99–100; Sportiche et al. 2014:62–8; Müller 2016:10, 16–7 The next examples demonstrate that coordination identifies individual words as constituents:
Drunks could put off the customers. (a) [Drunks] and [bums] could put off the customers. (b) Drunks [could] and [would] put off the customers. (c) Drunks could [put off] and [drive away] the customers. (d) Drunks could put off the [customers] and [neighbors].
The square brackets mark the conjuncts of the coordinate structures. Based on these data, one might assume that drunks, could, put off, and customers are constituents in the test sentence because these strings can be coordinated with bums, would, drive away, and neighbors, respectively. Coordination also identifies multi-word strings as constituents:
(e) Drunks could put off [the customers] and [the neighbors]. (f) Drunks could [put off the customers] and [drive away the neighbors]. (g) Drunks [could put off the customers] and [would drive away the neighbors].
These data suggest that the customers, put off the customers, and could put off the customers are constituents in the test sentence.
Examples such as (a-g) are not controversial insofar as many theories of sentence structure readily view the strings tested in sentences (a-g) as constituents. However, additional data are problematic, since they suggest that certain strings are also constituents even though most theories of syntax do not acknowledge them as such, e.g.
(h) Drunks [could put off] and [would really annoy] the customers. (i) Drunks could [put off these] and [piss off those] customers. (j) [Drunks could], and [they probably would], put off the customers.
These data suggest that could put off, put off these, and Drunks could are constituents in the test sentence. Most theories of syntax reject the notion that these strings are constituents, though. Data such as (h-j) are sometimes addressed in terms of the right node raising (RNR) mechanism.
The problem for the coordination test represented by examples (h-j) is compounded when one looks beyond the test sentence, for one quickly finds that coordination suggests that a wide range of strings are constituents that most theories of syntax do not acknowledge as such, e.g.
(k) Sam leaves [from home on Tuesday] and [from work on Wednesday]. (l) Sam leaves [from home on Tuesday on his bicycle] and [from work on Wednesday in his car]. (m) Sam leaves [from home on Tuesday], and [from work].
The strings from home on Tuesday and from home on Tuesday on his bicycle are not viewed as constituents in most theories of syntax, and concerning sentence (m), it is very difficult there to even discern how one should delimit the conjuncts of the coordinate structure. The coordinate structures in (k-l) are sometimes characterized in terms of non-constituent conjuncts (NCC), and the instance of coordination in sentence (m) is sometimes discussed in terms of stripping and/or gapping.
Due to the difficulties suggested with examples (h-m), many grammarians view coordination skeptically regarding its value as a test for constituents. The discussion of the other tests for constituents below reveals that this skepticism is warranted, since coordination identifies many more strings as constituents than the other tests for constituents.The problems with coordination as a test for constituent structure have been pointed out in numerous places in the literature. See for instance Baker 1989:425; McCawley 1998:63; Adger 2003:125; Payne 2006:162; Kim and Sells 2008:22; Carnie 2010:21; Carnie 2013:100; Sportiche et al. 2014:66; Müller 2016:16-7.
Proform substitution (replacement) Proform substitution, or replacement, involves replacing the test string with the appropriate proform (e.g. pronoun, pro-verb, pro-adjective, etc.). Substitution normally involves using a definite proform 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 test string is likely a constituent:For examples of pro-form substitution used as a test for constituents, see Allerton 1979:113–4; Radford 1981:63–6; Atkinson et al. 1982:173–4; Radford 1988:78–81, 98–9; Thomas 1993:10–12; Napoli 1993:168; Ouhalla 1994:19; Radford 1997:109; Haegeman and Guéron 1999:46; Fromkin 2000:155–8; Lasnik 2000:9–10; Lobeck 2000:53–7; Börjars and Burridge 2001:24–5; van Valin 2001: 111–2; Poole 2002:29–31; Adger 2003:63; Radford 2004:71; Tallerman 2005:140–2; Haegeman 2006:74–9; Moravcsik 2006:123; Kim and Sells 2008:21–2; Culicover 2009:81; Carnie 2010:19–20; Quirk et al. 2010:75–7; Miller 2011:54–5; Sobin 2011:32; Carnie 2013:98; Denham and Lobeck 2013:262–5; Sportiche et al. 2014:50; Müller 2016:8.
Drunks could put off the customers. (a) They could put off the customers. (They = Drunks) (b) Drunks could put them off. (them = the customers; note that shifting of them and off has occurred here.) (c) Drunks could do it. (do it = put off the customers)
These examples suggest that Drunks, the customers, and put off the customers in the test sentence are constituents. An important aspect of the proform test is the fact that it fails to identify most subphrasal strings as constituents, e.g.
(d) *Drunks do so/it put off the customers (do so/it = could) (e) *Drunks could do so/it off the customers (do so/it = put) (f) *Drunks could put so/it the customers (so/it = off) (g) *Drunks could put off the them. (them = customers)
These examples suggest that the individual words could, put, off, and customers should not be viewed as constituents. This suggestion is of course controversial, since most theories of syntax assume that individual words are constituents by default. The conclusion one can reach based on such examples, however, is that proform substitution using a definite proform identifies phrasal constituents only; it fails to identify sub-phrasal strings as constituents.
Topicalization (fronting)