Auxiliary verb

In linguistics, an auxiliary verb is a verb that gives further semantic or syntactic information about a main or full verb. In English, the extra meaning provided by an auxiliary verb alters the basic meaning of the main verb to make it have one or more of the following functions: passive voice, progressive aspect, perfect aspect, modality, or emphasis. It is also called helping verb, helper verb, auxiliary verb, or verbal auxiliary, and abbreviated aux.

In English, every clause has a finite verb which consists of a main 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 main 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 subject is doing at the given (in this case present) time without indicating completion, whereas “I ride my bicycle” is a temporally broader statement referring to something that occurs habitually in the past, present, and future. Similarly, “I was riding my bicycle” refers to the ongoing nature of what I was doing in the past, without viewing it in its entirety through completion, whereas “I rode my bicycle” refers either to a single past act viewed in its entirety through completion or to a past act that occurred habitually.

Perfect aspect

The auxiliary verb have is used with a past participle to indicate perfect aspect: a current state experienced by the subject as a result of a past action or state. For example, in “I have visited Paris” the current state is one of having a Paris visit in one’s past, while the past action is visiting Paris. The past action may be ongoing, as in “I have been studying all night”. An example involving the result of a past state rather than a past action is “I have known that for a long time”, in which the past state still exists (I still know it) along with the resultant state (I am someone who knew that at some past time). An example involving the result of a past state that no longer exists is “I have felt bad in the past, but not recently”. The alternative use of had instead of have places the perspective from which the resultant state is viewed in the past: “By 1985 I had visited Paris” describes the 1985 state of having a prior Paris visit.


Modality means the attitude of the speaker to the action or state being expressed, in terms of either degree of probability (“The sun must be down already”, “The sun should be down already”, “The sun may be down already”, “The sun might be down already”), ability (“I can speak French”), or permission or obligation (“You must go now”, “You should go now”, “You may go now”). See modal verb and English modal verb.

Dummy function

Do, does, or did plays a dummy (place-filling) role in transforming affirmative sentences with simple (one-word) verbs into questions or negatives. If an affirmative statement has a two-word verb (auxiliary plus main verb), a question is formed by inverting the order of the subject and the auxiliary, and a negative is formed by inserting “not” between the auxiliary and the main verb. But in the absence of an auxiliary verb, the dummy “do” is inserted as an auxiliary for either of these purposes: for example, “I go” → “Do I go?”, “I do not go”; “He goes” → “Does he go?”, “He does not go”; “I went” → “Did I go?”, “I did not go”.


The auxiliaries do, does, and did are also used for emphasis in positive declarative statements in which the verb otherwise contains only one word: “I do like this shirt!”, “He does like this shirt”, “I did like that shirt”.

Properties of the English auxiliary verb


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?.


Auxiliaries invert to form questions:

  • “You will come.”
  • “Will you come?”


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?”

Similar negative auxiliary verbs are found in Nivkh and the Salish and Chimakuan languages formerly spoken in northwestern North America. Salish and Chimakuan languages also have interrogative auxiliary verbs that form questions in the same manner as negative verbs do negated statements.

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