Prepositions form a closed word class, although there are also certain phrases that serve as prepositions, such as in front of.
A single preposition may have a variety of meanings, often including temporal, spatial and abstract. Many words that are prepositions can also serve as adverbs. Examples of common English prepositions (including phrasal instances) are of, in, on, over, under, to, from, with, in front of, behind, opposite, by, before, after, during, through, in spite of or despite, between, among, etc.
A preposition is usually used with a noun phrase as its complement.
A preposition together with its complement is called a prepositional phrase.
Examples are in England, under the table, after six pleasant weeks, between the land and the sea.
A prepositional phrase can be used as a complement or post-modifier of a noun in a noun phrase, as in the man in the car, the start of the fight; as a complement of a verb or adjective, as in deal with the problem, proud of oneself; or generally as an adverb phrase.
English allows the use of "stranded" prepositions. This can occur in interrogative and relative clauses, where the interrogative or relative pronoun that is the preposition's complement is moved to the start (fronted), leaving the preposition in place. This kind of structure is avoided in some kinds of formal English.
- What are you talking about? (Possible alternative version: About what are you talking?)
- The song that you were listening to ... (more formal: The song to which you were listening ...)
Notice that in the second example the relative pronoun that could be omitted.
Stranded prepositions can also arise in passive voice constructions and other uses of passive past participial phrases, where the complement in a prepositional phrase can become zero in the same way that a verb's direct object would: it was looked at; I will be operated on; get your teeth seen to.
The same can happen in certain uses of infinitive phrases: he is nice to talk to; this is the page to make copies of.