In grammar, a preposition is a word that establishes a relationship between what is called its object (usually a noun phrase) and some other part of the sentence.
Examples (with the preposition highlighted):
- My coat is on the sofa.
- I knitted throughout the day.
- They will not be finished until lunchtime.
- The keys are between the cushions.
- A man hid behind the door.
The preposition and its object make up a prepositional phrase, which can be used to modify noun phrases and verb phrases in the manner of adjectives and adverbs. For example, in the sentence "He has a can of lemonade", the prepositional phrase of lemonade is used to modify the noun can. In the sentence "The girl sat in the chair", the prepositional phrase in the chair modifies the verb sat.
Although the canonical object of a preposition is a noun phrase, there are cases in which another kind of phrase forms a prepositions object. For instance, in the sentence "Come out from under the bed", the object of the preposition from is another prepositional phrase, under the bed. Furthermore, according to some analyses, in the sentence "I opened the door before he walked in", before is not a conjunction but rather a preposition whose object is a full sentence (he walked in).
In some languages, such as Japanese, prepositions come after the noun and hence are called postpositions. In some inflected languages, prepositions are not separate words; their function is instead performed by a system of inflections on nouns called cases or declension.
In English usage, sentences ending with prepositions have been controversial, though less so in recent years. It is often difficult to avoid ending a sentence with a preposition without making is sound pompous or odd. For example, "What did you talk to him about" would have to become "About what did you talk to him?" and "This is something we will not put up with" would have to become "This is something up with which we will not put".