A Corpus-based Syntactic Analysis of Two-termed Unlike Coordination (2021)

Abstract: Coordination is a phenomenon of language that conjoins two or more terms or phrases using a coordinating conjunction. Although coordination has been explored extensively in the linguistics literature, the rules and constraints that govern its structure are still largely elusive and widely debated amongst linguists. This paper presents a study of two-termed unlike coordinations in particular, where the two conjuncts of the coordination phrase form valid constituents but have distinct categories. We conducted a syntactic analysis of the phrasal categories that can be conjoined in such unlike coordinations through a computational corpus-based approach, utilizing the Corpus of Contemporary American English (COCA) as the main data source, as well as the Penn Treebank (PTB). The results show that the two conjuncts within unlike coordinations display different properties based on their position, supporting an antisymmetric view of the structure of coordination. This research provides new data and perspectives through the use of statistical techniques that can help shape future theories and models of coordination.

## introduction 1.motivation coordination is a phenomenon of language that conjoins two or more terms or phrases. the terms or phrases that are grouped in coordination phrases are normally called conjuncts, and they are often conjoined by a coordinating conjunction, such as and, or, but, or nor. a common assumption in the linguistics literature is that two elements may only be coordinated if they share the same syntactic category, as in (1). for example, in (1a), the two conjuncts being coordinated are "the chicken" and "the rice," which share the same syntactic category of noun phrase (np). the assumption that the conjuncts of a coordination phrase will always have the same category is known as the law of the coordination of likes (lcl) @xcite . the lcl explains why many instances of coordination are ungrammatical, such as the coordination of a prepositional phrase (pp) and a clause (cp) shown in (2) @xcite . the scene that i wrote was in chicago. c. * the scene [ pp of the movie] and [ cp that i wrote] was in chicago. even though the prepositional phrase and the clause are both grammatical when standing alone within the context sentence, as in (2a) and (2b), their coordination in (2c) is ungrammatical, supposedly because of the lcl. however, several examples of syntactically unlike coordination can be found in english, such as the examples in (3) @xcite . pat is [ np a republican] and [ ap proud of it]. b. john is [ ap healthy] and [ pp in good shape]. c. that was [ np a rude remark] and [ pp in very bad taste]. in the above examples, the two conjuncts within each coordination phrase do not share the same syntactic category. in these cases, the lcl seems to be too restrictive. yet, there are also cases in which the lcl is not restrictive enough-a coordination phrase can still be ungrammatical even if its conjuncts have the same syntactic category @xcite . example (4a) contains the coordination of two prepositional phrases, and ( 4b ) contains the coordination of two adverbs. despite the two conjuncts having like categories, these examples result in ungrammatical sentences. semantics seems to play a role in the acceptability of coordinations as well; a stronger version of the lcl requires that conjuncts must also be alike in their semantic function. for example, in (4a), the first prepositional phrase "with his mother" expresses accompaniment, whereas the second "with good appetite" expresses manner @xcite . however, identifying and articulating rigorous rules that predict all grammatical possibilities of coordination has been a difficult task for linguists, and as a result, the underlying syntactic structure of coordination phrases has been elusive. ## background and related work capturing the structure of coordination has been a difficult problem in many theories of syntax. a flat, multi-headed structure was proposed in earlier theories, in which two or more lexical heads share the same phrase-level projection, as in the templates shown in figure 1 @xcite . this theory captures the intuitive idea that the coordination of two nps is an np, that the coordination of two vps is a vp, etc. an example of a two-termed coordination of nps is provided in (5). we use cc as the name for the functional category of coordinating conjunctions, which is also the label used in the ptb. there are several problems with this view, but the problem we are most concerned with relates to the aforementioned counterexamples to the lcl, restated below in (6). in fact, the lcl was formulated due to this proposal for the syntax of coordination. coordination was said to denote a relation between two (or more) elements that are "hierarchically equal" in that neither of the elements is more prominent than the other, leading to a symmetrical and flat vision of coordination structures @xcite . since conjuncts were assumed to be symmetrical and equal in status, it followed that they must share the same syntactic category to be grammatically coordinated. one proposal that seems to address the existence of the unlike category coordinations seen in ( 6 ) is bowers's pred (predicate) functional category @xcite . on top of the nps, aps, and pps being coordinated in these sentences, there is another level of structure. bowers suggests that a null pred head selects an np, ap, or pp as its complement, forming a predicate phrase (predp). thus, unlike coordinations are actually like coordinations in disguise-all conjuncts have the category of predp. predps are complements of the copula be in these sentences, as made apparent in (7). other proposals dodge the problem of unlike coordination entirely by making the coordinating conjunction the head of its own coordination phrase (ccp). one example of such a theory is shown in (9). here, conjuncts are specifiers and complements of the head conjunction @xcite . with such a construction, the categories of the conjuncts by themselves do not pose a restriction on the possibility of coordination. thus, such theories do not have anything to say about the lcl, but they are still problematic in that they over-generate; no combinations of categories are prohibited. ## approach we approached the task of capturing the structure of two-termed coordination by conducting a computational syntactic analysis on a large quantity of corpus data. our primary data source is the corpus of contemporary american english (coca) @xcite , and our additional data source is the penn treebank (ptb) augmented with ficler and goldberg's ptb coordination annotation extension @xcite . we extracted coordination phrases from both of these datasets and performed a quantitative syntactic analysis using the constituency parses of the sentences within both texts. this approach has a few advantages over previous work. much of the research that has shaped current theories of coordination have relied on the acceptability judgments of a few individuals, usually the author(s). by using corpus data, we gain an understanding of coordination on a much larger scale and emphasize empirical rather than intuitive judgments. we can also investigate differences in the patterns we identify based on the genre from which a coordination was found or the conjunction it contains. ## results in our analyses, we employ the chi-square (χ 2 ) tests, which determine whether a set of observed frequencies deviate significantly from a set of expected frequencies. we consider p-values less than 0.05 to be statistically significant. since our sample sizes are very large, we conduct additional posttests to accompany any statistically significant results. we use cramer's v to measure strength of association ( ## evaluation a portion of the data we have presented in the previous section was gathered through the use of a constituency parser to identify coordination phrases. while the berkeley neural parser is state-of-the-art, no parser is perfect, especially concerning coordination disambiguation. furthermore, there are additional types of coordination structures that we do not consider, including non-constituent coordination and gapping. in non-constituent coordination, each conjunct in a coordination phrase does not form its own constituent under traditional theories of clause structure, as shown in example ( 10 ). gapping is the phenomenon in which a phrase is coordinated with another phrase that seems to be missing some material, as shown in ( 11 ). while this paper only seeks to analyze the coordination of constituents and does not consider these additional types of coordination, they still pose challenges in the identification and labeling of coordination phrases by parsers. we have conducted an evaluation plan in which human raters manually assessed a random sample of unlike coordinations to estimate an error rate for each type of category combination. each type of unlike coordination was assigned a score based on the judgments of three independent raters. a single rater contributes to the score by providing the percentage of samples in which they agreed with the parser's labels. the overall score for that type of coordination is then assigned by taking the mean of the three raters' scores. the scores for each type of unlike coordination are enumerated in fleiss' kappa showed that, among the three raters, there was fair agreement in their judgments, κ = .291 (95% ci [.271, .312]), @xmath0.001. the strength of agreement is determined based on the cohen's kappa coefficient ( ## conclusion this paper approached the problem of understanding the syntax of two-termed coordination phrases through a computational corpus analysis. previous research has not attempted a thorough analysis of coordination based on english corpora, instead relying on intuitive acceptability judgments to inform their theories. we conducted a syntactic analysis by extracting coordination phrases from the corpus of contemporary american english and the penn treebank, and we investigated the most common unlike coordinations and the syntactic categories that appeared in either of the two conjunct positions. some of the findings from this project have interesting implications for coordination and syntax as a whole. the high frequency of coordinations of noun phrases with subordinate clauses provides further proof that noun phrases and clauses share similar syntactic distributions and may be structurally defined as determiner phrases. the tendency for first conjuncts to be shorter constituents and second conjuncts to be longer ones might suggest that shifting occurs in coordination structures as well. one of the main takeaways from these results is that there are evident syntactic distinctions between the two conjuncts of a coordination phrase, which support theories that posit an antisymmetric account for the structure of coordination.