12.3.3 The Noun Phrase

Our $ \mathcal{L}_0 $ grammar introduced three of the most frequent types of noun phrases that occur in English: pronouns, proper-nouns and the NP $ \rightarrow $ Det Nominal construction.

While pronouns and proper-nouns can be complex in their own ways, the central focus of this section is on the last type since that is where the bulk of the syntactic complexity resides. We can view these noun phrases consisting of a head, the central noun in the noun phrase, along with various modifiers that can occur before or after the head noun. Let's take a close look at the various parts.

The Determiner

Noun phrases can begin with simple lexical determiners, as in the following examples:

a stop the flights this flight

those flights any flights some flights

The role of the determiner in English noun phrases can also be filled by more complex expressions, as follows:

United's flight

United's pilot's union

Denver's mayor's mother's canceled flight

In these examples, the role of the determiner is filled by a possessive expression consisting of a noun phrase followed by an 's as a possessive marker, as in the following rule.

$$ Det\ \to\ N P^{\prime}s $$

The fact that this rule is recursive (since an NP can start with a Det), will help us model the latter two examples above, where a sequence of possessive expressions serves as a determiner.

There are also circumstances under which determiners are optional in English. For example, determiners may be omitted if the noun they modify is plural:

(12.5) Show me flights from San Francisco to Denver on weekdays

As we saw in Ch. 5, mass nouns also don't require determination. Recall that mass nouns often (not always) involve something that is treated like a substance (including e.g., water and snow), don't take the indefinite article "a", and don't tend to pluralize. Many abstract nouns are mass nouns (music, homework). Mass nouns in the ATIS domain include breakfast, lunch, and dinner:

(12.6) Does this flight serve dinner?

Exercise 12.4 asks the reader to represent this fact in the CFG formalism.

The Nominal

The nominal construction follows the determiner and contains any pre- and post-head noun modifiers. As indicated in grammar $ \mathcal{L}_{0} $, in its simplest form a nominal can consist of a single noun.

$$ Nominal\ \rightarrow\ Noun $$

As we'll see, this rule also provides the basis for the bottom of various recursive rules used to capture more complex nominal constructions.

Before the Head Noun

A number of different kinds of word classes can appear before the head noun (the “postdeterminers”) in a nominal. These include cardinal numbers, ordinal numbers, and quantifiers. Examples of cardinal numbers:

two friends one stop

Ordinal numbers include first, second, third, and so on, but also words like next, last, past, other, and another:

the first one the next day the second leg the last flight the other American flight

Some quantifiers (many, (a) few, several) occur only with plural count nouns: many fares

The quantifiers much and a little occur only with noncount nouns. Adjectives occur after quantifiers but before nouns.

a first-class fare a nonstop flight

the longest layover the earliest lunch flight

Adjectives can also be grouped into a phrase called an adjective phrase or AP. APs can have an adverb before the adjective (see Ch. 5 for definitions of adjectives and adverbs):

the least expensive fare

We can combine all the options for prenominal modifiers with one rule as follows:

NP $ \rightarrow $ (Det) (Card) (Ord) (Quant) (AP) Nominal

This simplified noun phrase rule has a flatter structure and hence is simpler than would be assumed by most modern generative theories of grammar; as we will see in Sec. 12.4, flat structures are often used for simplicity in computational applications (and indeed, there is no universally agreed-upon internal constituency for the noun phrase).

Note the use of parentheses “()” to mark optional constituents. A rule with one set of parentheses is really a shorthand for two rules, one with the parentheses, one without.

After the Head Noun

A head noun can be followed by postmodifiers. Three kinds of nominal postmodifiers are very common in English:

prepositional phrases all flights from Cleveland

non-finite clauses any flights arriving after eleven a.m.

relative clauses a flight that serves breakfast

Prepositional phrase postmodifiers are particularly common in the ATIS corpus, since they are used to mark the origin and destination of flights. Here are some examples, with brackets inserted to show the boundaries of each PP; note that more than one PP can be strung together:

any stopovers [for Delta seven fifty one]

all flights [from Cleveland] to Newark

arrival [in San Jose] [before seven p.m.]

a reservation [on flight six oh six] [from Tampa] [to Montreal]

Here's a new nominal rule to account for postnominal PPs:

Nominal $ \rightarrow $ Nominal PP

The three most common kinds of non-finite postmodifiers are the gerundive (-ing), -ed, and infinitive forms.

Gerundive postmodifiers are so-called because they consist of a verb phrase that begins with the gerundive (-ing) form of the verb. In the following examples, the verb phrases happen to all have only prepositional phrases after the verb, but in general this verb phrase can have anything in it (anything, that is, which is semantically and syntactically compatible with the gerund verb).

any of those [leaving on Thursday]

any flights [arriving after eleven a.m.]

flights [arriving within thirty minutes of each other]

We can define the Nominals with gerundive modifiers as follows, making use of a new non-terminal GerundVP:

Nominal $ \rightarrow $ Nominal GerundVP

We can make rules for GerundVP constituents by duplicating all of our VP productions, substituting GerundV for V.

GerundVP $ \rightarrow $ GerundVNP

GerundV PP | GerundV | GerundV NP PP

GerundV can then be defined as:

$$ {G e r u n d V~}\to{~b e i n g~|~a r r i v i n g~|~l e a v i n g~|~...} $$

The phrases in italics below are examples of the two other common kinds of non-finite clauses, infinitives and -ed forms:

the last flight to arrive in Boston

I need to have dinner served

Which is the aircraft used by this flight?

A postnominal relative clause (more correctly a restrictive relative clause), is a clause that often begins with a relative pronoun (that and who are the most common). The relative pronoun functions as the subject of the embedded verb (is a subject relative) in the following examples:

a flight that serves breakfast

flights that leave in the morning

the United flight that arrives in San Jose around ten p.m.

the one that leaves at ten thirty five

We might add rules like the following to deal with these:

Nominal $ \rightarrow $ Nominal RelClause

$$ RelClause\ \to\ (who\ \mid\ that)\ VP $$

The relative pronoun may also function as the object of the embedded verb, as in the following example; we leave as an exercise for the reader writing grammar rules for more complex relative clauses of this kind.

the earliest American Airlines flight that I can get

Various postnominal modifiers can be combined, as the following examples show:

a flight [from Phoenix to Detroit] [leaving Monday evening]

I need a flight [to Seattle] [leaving from Baltimore] [making a stop in Minneapolis]

evening flights [from Nashville to Houston] [that serve dinner]

a friend [living in Denver] [that would like to visit me here in Washington DC]

PREDETERMINERS

Before the Noun Phrase

Word classes that modify and appear before NPs are called predetermineders. Many of these have to do with number or amount; a common predeterminediner is all:

all the flights ___ all flights ___ all non-stop flights

The example noun phrase given in Fig. 12.5 illustrates some of the complexity that arises when these rules are combined.