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The Phrase Structure Rules of English
We can best begin the description of English phrase structure rules by taking a very simple example of a phrase structure of grammar, such as is given in (1) below:
1. (i) S: NP VP
(ii) VP: V NP
(iii) NP: Det N
(iv) Det: the
(v) N: cat, mouse
(vi) V: catch
This grammar consists of six phrase structure rules. (‘Phrase structure’ will henceforth be abbreviated ‘PS’). Each rule is an instruction to ‘rewrite’ the symbol on the left of the arrow as the string of one or more symbols given on the right. The symbols used in the grammar are divided into two discrete sets (apart from the arrow): non-terminal symbols occur on the left of some rule or rules, terminal ones do not. The terminal symbols represent morphemes, the non-terminal ones syntactic categories (with the following abbreviations: S = sentence, NP = noun phrase, VP = verb phrase, V = verb, Det = determiner, N = noun).
Such rules permit the construction of sentences in a purely mechanical way in accordance with our goal of complete explicitness. The procedure is illustrated in (2), where the succession of ‘strings’ of symbols constitutes what is called a PS derivation.
2. (i) #S#
(ii) #NP VP#
(iii) #NP V NP#
(iv) #Det N V NP#
(v) #Det N V Det N#
In the above, # indicates sentence boundary. S is designated as the initial symbol of the grammar, reflecting the fact that we are concerned with devising a grammar to generate sentences. Thus all PS derivations generated by this grammar (and others we shall consider) have #S# as the first line. Each subsequent line in a derivation derives from the one preceding it by one application of a PS rule. Line (2ii) derives from line (2i) by rewriting S as NP followed by VP according to rule (1i); line (2iii) derives from (2ii) by rewriting VP as V NP by rule (1ii), the initial NP of (2ii) being simply copied down unchanged into line (iii), and so on. In moving from one line to the next, we replace just one symbol and copy the remainder unchanged. A derivation is complete, or terminated, when its last line contains no non-terminal symbols. The last line of the derivation can then be converted into the appropriate phonological representation by means of morphophonemic rules corresponding to The cat caught the mouse.
In addition to generating a set of sentences, such a grammar automatically assigns a structure to each. For example, the structure assigned to the sentence The cat caught the mouse by grammar (1) may be represented in a tree diagram (3):
3.
S
VP
NP
Det
caught
This kind of representation is known as a phrase marker (henceforth ‘PM’). The phrase marker is a set of strings that assigns a structural interpretation to a terminal string (the string of lexical categories that terminates the phrase structure derivation).
Apart from using a tree diagram, phrase markers can be represented bracketing. In a labeled bracketing, whole constituents are enclosed in square brackets. Such constituents are labeled according to the name of the constituent in which they are enclosed. It should be noted that once a bracket is opened, it must be closed; otherwise, the analysis will be incorrect. Consider our example (3).
3. The cat caught the mouse
[s[NP[The] [cat]] [VP[caught] [NP[the] [mouse]]]]
Det N v Det N
The grammar discussed so far can generate sentences such as 4(a), (b), (c) but not 5(a), (b), (c):
4. (a) The man has the book
(b) John passed the exam
(c) Fali owns a truck
5. (a) The man will have the book (b) John may pass the exam (c) Fali can own a truck
Is it possible to make up a new rule that will generate the sentences in (5)? Indeed, it is, and this new rule is formulated as (6):
6. S: NP INFL VP
As in (1) above, S = sentence, NP = noun phrase, INFL = inflection (this is the same as Aux = auxiliary used in some texts), VP = verb phrase. Each of these phrasal categories is broken down into its component parts as illustrated in (1). As can be observed, the only difference with (1) is the addition of the phrasal category INFL. This can be expanded to give (7):
7. INFL: Tense (M) (have + en) (be + ing)
In (7) tense could be present or past, M = modal (will, would, can, could, shall, should, may, might, etc.). Brackets still indicate optionality.
We can, thus, represent 5(a) in a tree diagram as follows:
5. (a) The man will have the book
S
Note that have + en and be + ing are optional elements; hence they are not represented on the tree. If they are present as in 8(a) and 8(b), they will be represented as shown below:
8. (a) John may have passed the exam
(b) Fali may have been doing the work
INFL
NP INFL
NP
Tense doing the work
Modal
N
applied, we now have the
Dominance Relations
Before we consider how lexical items are introduced into phrase markers, it will be useful to discuss the relations between the elements in phrase markers. The relation between a category and its constituents is called dominance. That is, a category dominates all of its constituents. For example, the category VP in (3) dominates the category V, NP, Det, and N. However, the relation between VP and NP is different from the relation between VP and N. VP immediately dominates NP, but it does not immediately dominate N since another category, NP, intervenes between VP and N. We may say that a category X mandates category Y when X dominates Y and every other category dominating Y dominates X. When X immediately dominates Y, then Y is an immediate constituent of X.
In example (3) above, both NP and N are constituents of VP, but only NP is an immediate constituent of VP. Dominance relations between categories in a structural description determine the hierarchical structure of sentences. If two categories in a phrase marker are not in dominance relation, then they are in a precedence relation, for example, the subject NP in (3) precedes VP. Precedence relations determine the linear (left-to-right) ordering of elements in the phrase marker and hence determine the linear structure of sentences.
In terms of tree diagrams, two kinds of branching are possible: unary branching (where a category immediately dominates only one constituent) and n-ary branching (where a category has two or more immediate constituents). When a category has just two immediate constituents, it constitutes an instance of binary branching. A node is a point on the phrase marker where there is a category label. This category label can be phrasal (e.g. NP, VP) or lexical (e.g. N, V)
SYNTACTIC ANALYSIS
The process of syntactic analysis involves the application of phrase structure rules to a string of words to determine its structure. This process can be illustrated using the sentence "The man will have the book."
1. Start with the initial symbol S, which represents a sentence.
2. Apply the rule S -> NP INFL VP to expand S into NP INFL VP.
3. Apply the rule NP -> Det N to expand NP into Det N.
4. Apply the rule Det -> the to expand Det into the.
5. Apply the rule N -> man to expand N into man.
6. Apply the rule INFL -> will to expand INFL into will.
7. Apply the rule VP -> V NP to expand VP into V NP.
8. Apply the rule V -> have to expand V into have.
9. Apply the rule NP -> Det N to expand NP into Det N.
10. Apply the rule Det -> the to expand Det into the.
11. Apply the rule N -> book to expand N into book.
After applying these rules, we have derived the sentence structure:
S
NP INFL VP
Det N will VP
the man have NP
Det N
the book
This structure represents the hierarchical relationship between the words in the sentence, showing how they combine to form phrases and ultimately the complete sentence.
SUMMARY
Phrase structure rules are essential in understanding the syntactic structure of sentences in English. They provide a systematic way to analyze the structure of sentences, starting from basic categories like nouns and verbs and building up to complex sentences. By applying phrase structure rules, linguists and language learners can gain insights into the underlying structure of language and how words combine to form meaningful sentences. Understanding these rules is fundamental to understanding the grammar of any language.
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