A "preposition phrase" or "prepositional phrase" (PP) is a phrase headed by a preposition such as "at", "on", "across", or "before".
Prepositions and preposition phrases
The term pre-position literally means "positioned before", and this comes from the traditional analysis in which a preposition always comes before a noun phrase. For example:
To the store
Here, the preposition to comes before the noun phrase the store, which it takes as a complement. The preposition and its complement together form a preposition phrase.
A preposition phrase (PP), then, is a phrase headed by a preposition, such as at, on, across, or before. This is also commonly referred to as a prepositional phrase. The difference in terminology is small, but the shorter term "preposition phrase" is more in line with how we describe other phrases:
- A noun phrase (NP) is a phrase headed by a noun (not a nominal phrase)
- A verb phrase (VP) is a phrase headed by a verb (not a verbal phrase)
- A preposition phrase (PP) is a phrase headed by a preposition (not a prepositional phrase)
And so on.
Preposition phrases in modern grammar
In modern grammar, such as that put forth in The Cambridge Grammar of the English Language, the requirements for a PP are considerably relaxed. First, a preposition is no longer required to appear in front of its complement. Second, a preposition can take many kinds of complement or none at all. That means we have a lot more types of PP in modern grammar than in traditional grammar. Here are examples of the six types of complements a preposition can take:
A noun phrase:
It was [ under [ the table ]NP ]PP
Another preposition phrase:
I waited [ until [ after she left ]PP ]PP
A predicative complement:
I think of him [ as [ a friend ]PC ]PP
An adverb phrase, although only a few combinations are possible:
I hadn't realized that [ till [ recently ]AdvP ]PP
An entire clause:
I ate the cake [ because [ I was hungry ]Clause ]PP
Or nothing at all:
I'm sure that business will pick [ up ]PP
Some linguists refer to the prepositions in examples 1-5 above as transitive prepositions, while they refer to the complementless preposition in example 6 as an intransitive preposition. Intransitive prepositions are also referred to as particles, and this term is especially used by those who believe a preposition must have a complement.
Since traditional grammar requires that a preposition take a NP complement, the other uses are variously referred to as adverbs or as subordinating conjunctions.
Stranded prepositions and pre-position
Finally, an example in which the preposition is preceded by its complement:
Where are you headed to?
Because the complement where has been fronted, it appears before the preposition it belongs to. This is called a stranded preposition and was once frowned upon, but most authorities (descriptive and prescriptive alike) now agree that it's perfectly acceptable.