Phrase Head

See: Linguistic Phrase, Linguistic Component, Linguistic Phrase Modifier.

References

http://en.wikipedia.org/wiki/Phrase#Heads_and_dependents
- Most phrases have an important word defining the type and linguistic features of the phrase. This word is the head of the phrase and gives its name to the phrase category.^[1] The heads in the following phrases are in bold:

too slowly - Adverb phrase (AdvP)

very happy - Adjective phrase (AP)

the massive dinosaur - Noun phrase (NP)

watch TV - Verb phrase (VP)

The head can be distinguished from its dependents (the rest of the phrase other than the head) because the head of the phrase determines many of the grammatical features of the phrase as a whole. The examples just given show the five most commonly acknowledged types of phrases. Further phrase types can be assumed, although doing so is not common. For instance one might acknowledge subordinator phrases:

before that happened - Subordinator phrase (SP)

This "phrase" is more commonly classified as a full subordinate clause and therefore many grammars would not label it as a phrase. If one follows the reasoning of heads and dependents, however, then subordinate clauses should indeed qualify as phrases. Most theories of syntax see most if not all phrases as having a head. Sometimes, however, non-headed phrases are acknowledged. If a phrase lacks a head, it is known as exocentric, whereas phrases with heads are endocentric.