2 Constituency and Recursion in Language 3 4

6 Upon reflection, most people would agree that the words in a sen7 tence are not merely arranged like beads on a string. Rather, the 8 words group together to form coherent building blocks within a 9 sentence. Consider the sentence, The girl liked a boy. Intuitively, 10 the chunks the girl and liked a boy constitute the basic components 11 of this sentence (compared to a simple listing of the individual 12 words or alternative groupings, such as the girl liked and a boy). 13 Linguistically, these chunks comprise the two major constituents 14 of a sentence: a subject noun phrase (NP), the girl, and a verb 15 phrase (VP), liked a boy. Such phrasal constituents may contain 16 two types of syntactic elements: other phrasal constituents (e.g., 17 the NP a boy in the above VP) or lexical constituents (e.g., the 18 determiner the and the noun girl in the NP the girl). Both types of 19 constituent are typically defined distributionally using the so-called 20 replacement test: If a novel word or phrase has the same distribu21 tion as a word or phrase of a known constituent type—that is if the 22 former can be replaced by the latter—then they are the same type 23 of constituent. Thus, the lexical constituents the and a both belong 24 to the lexical category of determiners because they occur in similar 25 contexts and therefore can replace each other (e.g., A girl liked the 26 boy). Likewise, the girl and a boy belong to the same phrasal cate27 gory, NP, because they can be swapped around, as in A boy liked 28 the girl (note, however, that there may be semantic constraints on 29 constituent replacements. For example, replacing the animate sub30 ject NP the girl with the inanimate NP the chair yields the seman31 tically anomalous sentence, The chair liked a boy). 32 In linguistics, grammar rules and/or principles determine how 33 constituents can be put together to form sentences. For instance, 34 we can use the following phrase structure rules to describe the 35 relationship between the constituents in the example sentences 36 above: