An adposition appears before or after its complement, which may be a noun, noun phrase, pronoun, or other nominal phrase. Its function is to express the relationship of the given complement to another noun phrase, a verb phrase, or an adverbial (including time, location, instrument, or possession). Adpositions are heads of the phrases they belong to; nouns or NPs within these phrases are objects or complements of the adpositions.
Adpositions fall into two types, based on word order. Prepositions precede the complement, while postpositions follow the complement. The majority of languages display dominant or exclusive use of either prepositions or postpositions.
NoAdp: Adpositions do not exist.
Po: Only postpositions exist.
Popr: Postpositions are dominant, but prepositions also occur.
Pr: Only prepositions exist.
Prpo: Prepositions are dominant, but postpositions also occur.
PrPo: There is a relatively equal distribution of prepositions and postpositions.
 Other lexical and syntactic strategies may serve the same function, such as finite verbs, inflected nouns, case affixes, adverbial nominalizers, and clitics. Some of these may be derived from adpositions, but due to their bound forms do not constitute a separate word class. Adpositions form a distinct word class that is morphologically independent from verbs, inflected nouns, and adverbials.
 Languages that display the value NoAdp in parameter Person marking on adpositions will display the same value for this parameter.
 This includes languages that use the same adposition in both syntactic positions.