onphrase

Onphrase is a term used in some linguistic and computational linguistics literature to denote a prepositional phrase whose head is the preposition on and that serves a discourse-related function rather than primarily encoding spatial relation. In this sense, an onphrase can introduce topics, frame clauses, or mark stance, and it often operates at the periphery of a clause.

Typical onphrases include constructions such as on the topic of X, on the subject of Y, or on whether Z, where the phrase functions to set the scope or topic of discussion. Other instances are idiomatic adverbial on-phrases, such as on purpose or on second thought, which contribute to modality or stance rather than location. The classification is primarily used in syntactic and discourse analyses and is not universally standardized.

In computational linguistics and natural language processing, onphrase tagging may be used in parsing or information extraction to identify topical framing and discourse structure. It is related to the broader study of prepositional phrases and discourse markers. The term "onphrase" is mostly encountered in niche discussions and may vary in definition across sources.