Prepositions and postpositions, together called adpositions (or broadly, in English, simply prepositions), are a class of words used to express spatial or temporal relations (in, under, towards, before) or mark various semantic roles (of, for). A preposition or postposition typically combines with a noun phrase, this being called its complement, or sometimes object. A preposition comes before its complement; a postposition comes after its complement. English generally has prepositions rather than postpositions – words such as in, under and of preceding their objects, such as in England, under the table, of Jane – although there are a few exceptions including "ago" and "notwithstanding", as in "three days ago" and "financial limitations notwithstanding".
In linguistics, the grammar of a natural language is its set of structural constraints on speakers 'or writers' composition of clauses, phrases, and words. The term can also refer to the study of such constraints, a field that includes domains such as phonology, morphology, and syntax, often complemented by phonetics, semantics, and pragmatics. There are currently two different approaches to the study of grammar, traditional grammar and theoretical grammar.