prepositio

A prepositio, or preposition, is a small class of function words that introduces a prepositional phrase and expresses a relation between a noun phrase and another element in a sentence. The core structure is a preposition plus its complement, typically a noun phrase or pronoun, though in some languages the complement can be a clause. The term itself comes from Latin praepositio, meaning “placing before.”

Prepositions encode various semantic relations. Common categories include spatial or directional relations (in, on, under, toward, into), temporal relations (at, during, before, after), and other connections such as possession, means, cause, or agency (of, by, with, for, about). Many languages use multiword prepositions or phrasal expressions, such as in front of or on top of in English. Some languages, by contrast, rely more on case endings rather than prepositions to mark similar relations; others use postpositions or circumpositions.

Syntactically, a prepositional phrase (a preposition plus its complement) often functions as an adverbial modifier or as a postmodifier of a noun. It can indicate location or time for a verb, or attribute a property to a noun. The object of a preposition—its complement—must typically be a noun phrase or pronoun; pronoun objects may appear in specialized forms (to me, for him, etc.). Prepositions can form part of fixed expressions or idioms and may govern specific verbs or adjectives.

Cross-linguistically, the category is sometimes broader than “preposition”, including other adpositions (postpositions, circumpositions) depending on whether the expression precedes or follows its complement. The choice and use of prepositions are often idiosyncratic and taught as part of vocabulary and idiom learning.