In traditional grammar while, when, before, after, and since are conjunctions which join an adverb clause to an independent clause. The term adverbial clause is used because the clause adds time-related information about the verb and answers the question When? This added-on structure is called a dependent clause because it can not stand alone as a sentence. |
In current linguistic analysis – while, when, before, after, and since — are prepositions which take a clause as a complement: with a subject and a verb (while we were walking home) or with a gerund-participle (while walking home). Before and after additionally take a noun complement: (before me). The structure is called an adjunct because it is not required for completing the meaning of the sentence. (The sentence is complete without the prepositional phrase.) |
Azar & Hagen call these adverbial clauses or "time clauses" with no mention of a term for the connector. It is not clear whether while, when, before, after, and since are adverbs or conjunctions. "A time clause begins with such words as when, before after, as soon as, until, and while and includes a subjects and a verb. The time clause can come either at the beginning of the sentence or in the second part of the sentence…" (UUEG 4-3, Adverb clauses 17-2; Reduction 18-1) |
Huddleston & Pullum (2009) use the term "temporal location expressions". In their grammar description, they reassign a large number of items previously analyzed as adverbs after, as, as soon as, before, once, since while, and when to the category of Prepositions. The preposition is the head of the prepositional phrase (PP) which can be complemented by a noun phrase or a clause (with a subject and a verb, or a clause with a gerund-participle). (CaGEL 7.2.4, 8.63) |
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Swan (2009) refers to while, when, before, after, and since as conjunctions. (PEU 29.1, 30.1, 73, 97, 411.6, 510)
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after, because, though, if
— adverb clauses (UUEG 17.3-11) |
after, before, since, when, while\
— temporal location adjuncts.prepositions (CaGEL 7.2.4, 8 §6.3)
— conjunctions (PEU 29.1, 30.1, 73, 97, 411.6, 510)
— subordinator. adverbial clause (LGSWE 2.4.7.5)
— subordinator. adverbial clause (CoGEL 8.53, 15.28)
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