Phrase structure: heads, modifiers and complements
Noun, verb, adjective, adverb and prepositional phrases, the head that names each one, determiners, modifiers and complements, constituency tests, phrase structure rules and tree diagrams, and structural ambiguity.
Words come in groups
Read The new principal of our school arrived very early aloud and you will pause naturally after school. The sentence is not a string of nine separate words. It is two large groups, the new principal of our school and arrived very early, and each group is made of smaller groups. These groups are phrases. Phrase structure is the study of how words combine into phrases and phrases into sentences, and it explains things that word classes alone cannot: why very early moves as a unit, why I saw the man with the telescope has two meanings, and why *The principal new sounds wrong.
- Phrase – a group of words built around one central word and working as a single unit in a sentence.
- Head – the central word of a phrase; it decides the phrase's type and cannot normally be left out.
- Modifier – an optional element that describes or limits the head.
- Complement – an element the head needs or selects to complete its meaning, such as the object of a verb or preposition.
- Constituent – any word or group of words that works as a unit in the structure of a sentence.
1. The head names the phrase
Every phrase has a head, and the head's word class gives the phrase its name. In the very tall building the head is the noun building, so the whole group is a noun phrase. A one-word phrase is still a phrase: Maria in Maria sings is a noun phrase, and sings is a verb phrase.
| Phrase | Head | Examples (head in bold) | Typical jobs |
|---|---|---|---|
| Noun phrase (NP) | noun or pronoun | the old house; a cup of coffee; she | subject, object, complement, object of a preposition |
| Verb phrase (VP) | main verb | has been reading; gave me a book | predicate |
| Adjective phrase (AdjP) | adjective | very proud; afraid of the dark | modifies a noun; complement after a linking verb |
| Adverb phrase (AdvP) | adverb | quite slowly; very carefully indeed | modifies a verb, adjective, adverb or sentence |
| Prepositional phrase (PP) | preposition | in the morning; after the class | modifies a noun (adjectival) or a verb (adverbial) |
2. What surrounds the head
Determiners, pre-modifiers and post-modifiers in the NP
The noun phrase has the richest structure. Its order is fixed:
all those beautiful old stone churches in Bohol that survived the earthquake
- determiners: all those
- pre-modifiers: beautiful old stone (an opinion adjective, an age adjective and a noun used as a modifier)
- head: churches
- post-modifiers: in Bohol (a prepositional phrase) and that survived the earthquake (a relative clause)
Pre-modifying adjectives follow a usual order, roughly opinion – size – age – shape – colour – origin – material – purpose: a lovely small old round brown Spanish wooden prayer table. Few phrases stack more than three, but the order explains why a big red jeep sounds right and *a red big jeep does not.
Modifiers and complements
A complement completes the head; a modifier only adds detail. Compare:
- a student of physics – of physics is a complement: it says what is studied, and it must come next to the head (a student of physics from Leyte, not *a student from Leyte of physics).
- a student from Leyte – from Leyte is a modifier: it adds information and can be left out freely.
- In She put the book on the shelf, both the book and on the shelf are complements of put, since *She put the book is incomplete. In She read the book on the bus, on the bus is a modifier.
- Prepositions take a complement too, their object: in the box. A preposition with no object is behaving as an adverb or particle (Come in.).
Phrases inside phrases
Phrases embed. In the book on the table, the PP on the table contains its own NP, the table. In afraid of snakes, the AdjP contains a PP, which contains an NP. This embedding, called recursion, is what lets a finite grammar build endless sentences: the book on the table in the room at the end of the hall.
3. Finding constituents
How do you prove that a group of words is a phrase? Use the constituency tests.
- Substitution: a phrase can be replaced by a single word. The tall boy in red → he (an NP); in the library → there (a PP used as an adverbial); studied for the exam → did so (a VP).
- Movement: a phrase can move as a whole. She left after lunch → After lunch, she left. But *Lunch, she left after is odd, because lunch alone is not the adverbial.
- Question: a phrase can answer a question. Where did she leave it? – On the table.
- Coordination: only like phrases join with and: [the teacher] and [her students] (NP and NP).
4. Drawing the structure
Linguists show phrase structure with tree diagrams or labelled brackets, built from phrase structure rules such as these:
- S → NP VP (a sentence is a noun phrase followed by a verb phrase)
- NP → (Det) (AdjP) N (PP)
- VP → V (NP) (PP) (AdvP)
- PP → P NP
- AdjP → (Deg) Adj (PP), where Deg is a degree word such as very
Applied to The girl read a book in the library:
In a tree, S sits at the top and branches into NP and VP. The VP branches into V, NP and PP, and the PP into P and NP. Each branching point is a node, and a node that sits directly above another dominates it.
5. Structural ambiguity
When one string of words can be grouped in two ways, the sentence is structurally ambiguous. The words do not change; the brackets do.
- I saw the man with the telescope. [saw [the man] [with the telescope]] – I used the telescope; [saw [the man with the telescope]] – the man had it.
- old men and women – [old [men and women]] (both are old) or [[old men] and women] (only the men).
- the English history teacher – a teacher of English history, or a history teacher who is English.
Trees resolve the ambiguity by drawing each reading separately, which is why they are a useful teaching tool.
6. Notes for Filipino learners
- Modifier position. Filipino links modifiers with na/-ng and allows either order (magandang bahay, bahay na maganda). English adjectives go before the noun, so *a house beautiful is an error; adjective phrases with a complement go after it (a house full of books).
- Adjective order. *a red big jeep and *a wooden old chair break the size–age–colour–material order.
- Agreement with the head. The verb agrees with the head of the subject NP, not the nearest noun: The list of names is posted, not *are.