preposition

A preposition is a word that introduces a relationship between its complement and another element in a sentence. It usually sets up a link to a noun, pronoun, or noun phrase, and the combination forms a prepositional phrase.

Prepositions express various kinds of relations, most commonly spatial, temporal, and directional. Examples of spatial relations include in, on, under, beside; temporal relations include before, after, during, since; and other relations include with, by, about, for, to, of, due to. A prepositional phrase can modify a noun (an old house on the hill) or a verb (She walked around the corner).

A typical prepositional phrase consists of a preposition and its complement, which is usually a noun phrase or a pronoun. Some prepositions are multiword, forming complex prepositions such as in front of, because of, due to, or as well as. Prepositional phrases can function as adjectives, restricting a noun, or as adverbs, modifying a verb, an adjective, or another adverb.

In English, prepositions are often part of phrasal verbs, where a verb plus a preposition (or particle) creates a meaning distinct from the verb alone (look up, turn on, run into). The choice of preposition can influence meaning and is a common source of error for learners, especially when languages express relationships differently.

Across languages, prepositions are part of how grammatical relations are encoded, but not all languages use the same system. Some languages employ postpositions (which follow their complement) or circumpositions (surrounding a word). English relies primarily on prepositions to mark such relations, while other languages may use case marking or different syntactic devices to convey similar ideas.