12.3.5 The Verb Phrase and Subcategorization

The verb phrase consists of the verb and a number of other constituents. In the simple rules we have built so far, these other constituents include NPs and PPs and combinations of the two:

$$ \mathit{V P}\;\to\;\mathit{V e r b}\quad\mathrm{d i s a p p e a r} $$

\[VP\ \rightarrow\ \operatorname{Verb}\ NP\ \ \ \

$$ \textit{V P}\to\textit{V e r b}\textit{N P}\textit{P P}\quad\textit{l e a v e B o s t o n i n t h e m o r n i n g} $$

$$ VP\ \to\ \operatorname{V e r b}\ PP\ leaving~on\ \operatorname{T h u r s d a y} $$

Verb phrases can be significantly more complicated than this. Many other kinds of constituents can follow the verb, such as an entire embedded sentence. These are called sentential complements:

You [Vp [V said [s there were two flights that were the cheapest]]]

You [VP [V said [S you had a two hundred sixty six dollar fare]]

[VP [V Tell] [NP me] [S how to get from the airport in Philadelphia to downtown]]

I [VP [V think [s I would like to take the nine thirty flight]]

Here's a rule for these:

$$ V P\;\to\;V e r b\;S $$

Another potential constituent of the VP is another VP. This is often the case for verbs like want, would like, try, intend, need:

I want [VP to fly from Milwaukee to Orlando]

Hi, I want [VP to arrange three flights]

Hello, I'm trying [VP to find a flight that goes from Pittsburgh to Denver after two p.m.]

Recall from Ch. 5 that verbs can also be followed by particles, words that resemble a preposition but that combine with the verb to form a phrasal verb like take off. These particles are generally considered to be an integral part of the verb in a way that other post-verbal elements are not; phrasal verbs are treated as individual verbs composed of two words.

While a verb phrase can have many possible kinds of constituents, not every verb is compatible with every verb phrase. For example, the verb want can either be used with an NP complement (I want a flight …), or with an infinitive VP complement (I want to fly to …). By contrast, a verb like find cannot take this sort of VP complement. (*I found to fly to Dallas).

This idea that verbs are compatible with different kinds of complements is a very old one; traditional grammar distinguishes between transitive verbs like find, which take a direct object NP (I found a flight), and intransitive verbs like disappear, which do not (*I disappeared a flight).

Where traditional grammars subcategorize verbs into these two categories (transitive and intransitive), modern grammars distinguish as many as 100 subcategories. (In fact, tagsets for many such subcategorization frames exist; see Macleod et al. (1998) for the COMLEX tagset, Sanfilippo (1993) for the ACQUILEX tagset, and further discussion in Ch. 16). We say that a verb like find subcategorizes for an NP, while a verb like want subcategorizes for either an NP or a non-finite VP. We also call these constituents the complements of the verb (hence our use of the term sentential complement above). So we say that want can take a VP complement. These possible sets of complements are called the subcategorization frame for the verb. Another way of talking about the relation between the verb and these other constituents is to think of the verb as a logical predicate and the constituents as logical arguments of the predicate. So we can think of such predicate-argument relations as FIND(I, A FLIGHT), or WANT(I, TO FLY). We will talk more about this view of verbs and arguments in Ch. 17 when we talk about predicate calculus representations of verb semantics.

Subcategorization frames for a set of example verbs are given in Fig. 12.6. Note that a verb can subcategorize for a particular type of verb phrase, such as a verb phrase whose verb is an infinitive (VPto), or a verb phrase whose verb is a bare stem (uninfected: VPbrst). Note also that a single verb can take different subcategorization

| Frame | Verb | Example |

| --- | --- | --- |

| 0 | eat, sleep | I want to eat |

| NP | prefer, find, leave, | Find [NP the flight from Pittsburgh to Boston] |

| NP NP | show, give | Show [NP me] [NP airlines with flights from Pittsburgh] |

| PP $ _{from} $ PP $ _{to} $ | fly, travel | I would like to fly [PP from Boston] [PP to Philadelphia] |

| NP PP $ _{with} $ | help, load, | Can you help [NP me] [PP with a flight] |

| VP $ _{to} $ | prefer, want, need | I would prefer [VP $ _{to} $ to go by United airlines] |

| VP $ _{brst} $ | can, would, might | I can [VP $ _{brst} $ go from Boston] |

| S | mean | Does this mean [S AA has a hub in Boston]? |

| Figure 12.6 Subcategorization frames for a set of example verbs. | | |

frames. The verb find, for example, can take an NP NP frame (find me a flight) as well as an NP frame.

How can we represent the relation between verbs and their complements in a context-free grammar? One thing we could do is to do what we did with agreement features: make separate subtypes of the class Verb (Verb-with-NP-complement, Verb-with-Inf-VP-complement, Verb-with-S-complement, and so on):

$$ \mathbf{V e r b-w i t h-N P-c o m p l e m e n t}\;\to\;{\bf f i n d}\mid{\bf~l e a v e}\mid{\bf~r e p e a t}\mid\ldots $$

$$ \mathbf{V e r b-w i t h-S-c o m p l e m e n t}\;\to\;{t h i n k}\mid{~b e l i e v e~}\mid{~s a y~}\mid\;\ldots $$

$$ \mathbf{V e r b-w i t h-I n f-V P-c o m p l e m e n t}\;\to\;{w a n t}\mid{t r y}\mid{n e e d}\mid\ldots $$

Then each VP rule could be modified to require the appropriate verb subtype:

VP $ \rightarrow $ Verb-with-no-complement disappear

VP $ \rightarrow $ Verb-with-NP-comp NP prefer a morning flight

VP $ \rightarrow $ Verb-with-S-comp S said there were two flights

The problem with this approach, as with the same solution to the agreement feature problem, is a vast explosion in the number of rules. The standard solution to both of these problems is the feature structure, which will be introduced in Ch. 16 where we will also discuss the fact that nouns, adjectives, and prepositions can subcategorize for complements just as verbs can.