In linguistics, an auxiliary (also called helping verb, helper verb, auxiliary verb, or verbal auxiliary) 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 imparts 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).

There is a syntactic difference between an auxiliary verb and a full verb; that is, each has a different grammatical function within the sentence. In English, and in many other languages, there are 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 "Someone/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).

Contents [hide]
1 Functions of the English auxiliary verb
1.1 Passive voice
1.2 Progressive aspect
1.3 Perfect aspect
1.4 Modal
1.5 Dummy
1.6 Quasi-auxiliaries
2 Properties of the English auxiliary verb
2.1 Negation
2.2 Inversion
2.3 Emphasis
2.4 Ellipsis
2.5 Tag questions
2.6 In Scottish English
3 Other languages
4 See also
5 References

[edit] Functions of the English auxiliary verb

[edit] 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 due to this ambiguity, the verb get will sometimes be used colloquially instead of be in forming the passive voice, "at 8:25, the window got closed".

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

[edit] Perfect aspect
The auxiliary verb have is used with a past participle to form the perfect aspect; for example, the sentence "Peter has fallen in love" differs from "Peter fell in love" in that the former implies some connection to the present — likely that Peter is still in love — while the latter does not.

[edit] Modal
There are nine modal verbs: can, could, may, might, shall, should, will, would, and must. They differ from the other auxiliaries both in that they are defective verbs, and in that they can never function as main verbs. (There do exist main verbs can and will, but these are distinct.) They express the speaker's (or listener's) judgement or opinion at the moment of speaking. Some of the modal verbs have been seen as a conditional tense form in English.

Some schools of thought consider could to represent the past tense of can. However, according to Michael Lewis (The English Verb), this is not always true. "Could I get you something?" clearly is not expressing past time. Lewis instead suggests that could is a remote form of can. It is evident after re-examining the usage of could in this light that remoteness does describe the general meaning, e.g.

I couldn't do it. (remoteness of time)
It could happen. (remoteness of possibility)
Could you do me a favor? (remoteness of relationship)
The remaining modal auxiliaries can be viewed in this same manner. Lewis covers this area in detail in his book; see the References section.

[edit] Dummy
Because only auxiliaries can be inverted to form questions and only auxiliaries can take negation directly, a dummy auxiliary do is used for questions and negatives when only a full verb exists in the positive statement (i.e. there are no auxiliaries in the positive, non-interrogative form). The same dummy do is used for emphasis in the positive statement form. This is known as do-insertion.

For example, if the positive statement form is:

I know the way.
the interrogative, negative and emphatic forms are respectively:

Do I know the way?
I don't know the way.
I do know the way.
Compare this with:

Should I know the way?
I shouldn't know the way.
I should know the way.
The emphatic form would normally be marked by intonation or punctuation of 'I' or 'should'. With the first two forms it depends on context.

[edit] Quasi-auxiliaries
English contains many verb phrases that function as quasi-auxiliaries, such as be going to, used to, is about to. These quasi-auxiliaries require an infinitive. Others take a gerund (e.g. need, as in need fixing, in American English), past participle (e.g. get, as in get done), or other verb form.

In American English, go and come can be quasi-auxiliaries with nothing between them and the following verb phrases, but only in their plain forms: "Come show me", "I'll go get it", and "I had to come see for myself". This use can be regarded as ellipsis of and — the previous are equivalent to "Come and show me", "I'll go and get it", and "I had to come and see for myself" — and British English requires the and to be included, as does American English when the verb is not in its plain form: "I went and saw him." (It is also possible in both dialects for to to be used in place of and, though this typically has a slightly different sense.)

[edit] Properties of the English auxiliary verb
See also: English verbs

[edit] Negation
Auxiliaries take not (or n't) to form the negative, e.g. can't, won't, 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?'.

[edit] Inversion
Auxiliaries invert to form questions:

You will come.
Will you come?

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

I do like this beer!

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

I will go, but she won't [go].
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. (pro-VP: replaces sings in the kitchen)
John never sings in the kitchen, but Mary does in the shower. (pro-verb: replaces sings)

[edit] 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 come, will you?
You didn't eat, did you?

[edit] In Scottish English
An example was made famous by Hamish and Dougal

You'll have had your tea?
as a greeting. The implication is that I (having made the utterance) am not going to put myself in the position in which I would have to offer you tea, lest you had not had any.

More common, is the construction of the form

You'll not be wanting a drink?
uttered by a person who should offer you one but wishes not to

http://en.wikipedia.org