auxiliary verb

an auxiliary (also called helping verb, helper verb, auxiliary verb, or verbal auxiliary, abbreviated aux) is a verb functioning to give further semantic or syntactic information about the main or full verb following it. In English, the extra meaning an auxiliary verb alters the basic form of the main verb to have one or more of the following functions: passive, progressive, perfect, modal, or dummy.

In English, every clause has a finite verb which consists of a full verb (a non-auxiliary verb) and optionally one or more auxiliary verbs, each of which is a separate word. Examples of finite verbs include write (no auxiliary verb), have written (one auxiliary verb), and have been written (two auxiliary verbs). Many languages, including English, feature some verbs that can act either as auxiliary or as full verbs, such as be ("I am writing a letter" vs "I am a postman") and have ("I have written a letter" vs "I have a letter"). In the case of be, it is sometimes ambiguous whether it is auxiliary or not; for example, "the ice cream was melted" could mean either "something melted the ice cream" (in which case melt would be the main verb) or "the ice cream was mostly liquid" (in which case be would be the main verb).

The primary auxiliary verbs in English are to be and to have; other major ones include shall, will, may and can

Functions of the English auxiliary verb

Passive voice

The auxiliary verb be is used with a past participle to form the passive voice; for example, the clause "the door was opened" implies that someone (or something) opened it, without stating who (or what) it was. Because many past participles are also stative adjectives, the passive voice can sometimes be ambiguous; for example, "at 8:25, the window was closed" can be a passive-voice sentence meaning, "at 8:25, someone closed the window", or a non-passive-voice sentence meaning "at 8:25, the window was not open". Perhaps because of this ambiguity, the verb get is sometimes used colloquially instead of be in forming the passive voice, "at 8:25, the window got closed."

Progressive aspect

The auxiliary verb be is used with a present participle to form the progressive aspect; for example, "I am riding my bicycle" describes what the speaker is doing at the very moment of utterance, whereas "I ride my bicycle" is a temporally broader statement.

[edit] Properties of the English auxiliary verb

See also: English verbs

See also: List of English auxiliary verbs

Negation

Auxiliaries take not (or n't) to form the negative, e.g. cannot (can’t), will not (won’t), should not (shouldn’t), etc. In certain tenses, in questions, when a contracted auxiliary verb can be used, the position of the negative particle n't moves from the main verb to the auxiliary: cf. Does it not work? and Doesn't it work?. This has not always been the case as the following sentence from Jane Austen's 'Pride & Prejudice' indicates: 'The country is a vast deal pleasanter, is it not, Mr. Bingley?'.

Inversion

Auxiliaries invert to form questions:

• "You will come."
• "Will you come?"

Emphasis

The dummy auxiliary do is used for emphasis in positive statements (see above):

• "I do like this shirt!"

Ellipsis

Auxiliaries can appear alone where a main verb has been omitted, but is understood:

• "I will go, but she will not."

The verb do can act as a pro-VP (or occasionally a pro-verb) to avoid repetition:

• "John never sings in the kitchen, but Mary does."
• "John never sings in the kitchen, but Mary does in the shower."

Tag questions

Auxiliaries can be repeated at the end of a sentence, with negation added or removed, to form a tag question. In the event that the sentence did not use an auxiliary verb, a dummy auxiliary (a form of do) is used instead:

• "You will come, won't you?"
• "You ate, didn't you?"
• "You won't (will not) come, will you?"
• "You didn't (did not) eat, did you?"
• "You (do) know how to dance, don't you?"