Alex's Notes

English Grammar Rules (Jurafsky Martin)

As presented in Jurafsky Martin Chapter 12: Constituency Grammars

Sentence-level constructions

We start with some sentence-level constructions.

These are constructions that are in some sense complete. They may account for entire sentences, but they correspond more to the traditional notion of a clause, since \(S\) can appear on the right of a production rule too.

One way of thinking about these constructions as a “complete thought” is in terms of the parse tree. \(S\) is a node of the parse tree under which the main verb of the \(S\) has all of its arguments. So if you take “I prefer a morning flight” the verb “prefer” has both its subject and object arguments under the \(S\), the subject being a direct child of \(S\).

There are a large number of ways to construct English sentences, but four are particularly common and important:

Declarative Sentences

Declarative sentences. Their structure is typically \(S \rightarrow \; NP \; VP\), a subject noun followed by a verb phrase. Sentences of this kind have a great number of different uses. Some examples are:

  • I want a flight from Ontario to Chicago

  • The flight should be eleven a.m. tomorrow

  • The return flight should leave at around seven p.m.

Imperative Sentences

Imperative sentences. Their structure typically begins with a verb phrase with no subject, ie \(S \rightarrow \; VP\). Almost always used for commands and suggestions. Examples include:

  • Show the lowest fare.

  • Give me Sunday’s flights arriving in Las Vegas from New York City

  • List all flights between five and seven pm.

Yes-no Questions

Yes-No questions. These begin with an auxiliary verb, followed by a subject NP, followed by a VP, ie \(S \rightarrow \; Aux \; NP \; VP\). Note here that meaning depends on pragmatics, yes-no questions might not be questions at all but requests, as the third example here:

  • Do any of these flights have stops?

  • Does American’s flight eighteen twenty five serve dinner?

  • Can you give me the same information for United? (speaker expects more than ‘yes’!)

Wh-structures

Wh-structures are the most complex of the four. One of their constituents is a wh-phrase, ie a phrase including a wh-word (who, whose, when, where, what, which, how, why).

There are broadly two classes of sentence structures. In wh-subject-question sentences, the structure is identical to declarative sentences, except the first noun phrase contains some wh-word. The rule is $S → \; Wh-NP \; VP. Some examples:

  • What airlines frly from Burbank to Denver?

  • Which flights depart Burbank after noon and arrive by Denver by six p.m.?

  • Whose flights serve breakfast?

Wh-non-subject-question sentences are those where the wh-phrase is not the subject of the sentence, so the sentence has another subject. Here the auxiliary appears before the subject NP, and the rule becomes: \(S \rightarrow \;Wh-NP \; Aux \; NP \; VP\)

Examples include:

  • What flights do you have from Burbank to Tacoma?

This is our first encounter with long distance dependencies, the what flights is far away from the predicate, the verbe have, to which it relates.

We can either model this as a semantic relation, and leave it to semantic interpretation to figure out that “flights” is the argument to “have”.

Or we can model this as a syntactic relation, and include a small marker in our grammar called a trace or empty category after the verb.

Noun Phrases

The chapter then goes on to present Noun Phrases, focusing on the \(NP \rightarrow \; Det \; Nominal\) constructions.

Verb Phrases

The chapter then presents Verb Phrases

Coordination

The phrase types can be conjoined with conjunctions (and, but, or) to form larger constructions of the same type.

A coordinate noun phrase for example can consist of two other NPs separated by a conjunction: “the bear and the tiger”. A rule might be: \(NP \rightarrow \; NP \; and \; NP\) for example.

The ability to form coordinate phrases through conjunction is a test for constituency.

More generally we can have metarules like \(X \rightarrow \; X \; and \; X\) to indicate that any non-terminal type can be conjoined with the same type to yield a constituent of that type.

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