Do-support

do''-supportauxiliary ''doinsertedthe auxiliary is taken from the emphatic ''do'' formdostandard English has itsupportDo-periphrasis
Do-support (or do-insertion), in English grammar, is the use of the auxiliary verb do, including its inflected forms does and did, to form negated clauses and questions as well as other constructions in which subject–auxiliary inversion is required.wikipedia
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Auxiliary verb

auxiliaryauxiliary verbsauxiliaries
Do-support (or do-insertion), in English grammar, is the use of the auxiliary verb do, including its inflected forms does and did, to form negated clauses and questions as well as other constructions in which subject–auxiliary inversion is required.
– do is an auxiliary accompanying the main verb want, used here to form a question – see do-support.

Subject–auxiliary inversion

subject-auxiliary inversioninversioninversion of subject and auxiliary
Do-support (or do-insertion), in English grammar, is the use of the auxiliary verb do, including its inflected forms does and did, to form negated clauses and questions as well as other constructions in which subject–auxiliary inversion is required. The presence of an auxiliary (or copular) verb allows subject–auxiliary inversion to take place, as is required in most interrogative sentences in English. The same principles as for question formation apply to other clauses in which subject–auxiliary inversion is required, particularly after negative expressions and expressions involving only (negative inversion):
For details of the use of do, did and does for this and similar purposes, see do-support.

Question

wh-questionanswerquestions
Do-support (or do-insertion), in English grammar, is the use of the auxiliary verb do, including its inflected forms does and did, to form negated clauses and questions as well as other constructions in which subject–auxiliary inversion is required.
However, English allows such inversion only with a particular class of verbs (called auxiliary or special verbs), and thus sometimes requires the addition of an auxiliary do, does or did before inversion can take place ("He sings" → "Does he sing?") – for details see do-support.

Imperative mood

imperativeimperativesprohibitive
Do-support is required for negated imperatives even when the verb is the copula be:
(The present subjunctive always has the same form as the imperative, although it is negated differently – the imperative is negated using do not, as in "Don't touch me!"; see do-support.) The imperative form is understood as being in the second person (the subject pronoun you is usually omitted, although it can be included for emphasis), with no explicit indication of singular or plural.

Syntax

syntacticsyntacticalsyntactically
However, in the negated and inverted clauses referred to above, it is used because the rules of English syntax permit these constructions only when an auxiliary is present.
Do-support

English grammar

Englishgrammarthere is
Do-support (or do-insertion), in English grammar, is the use of the auxiliary verb do, including its inflected forms does and did, to form negated clauses and questions as well as other constructions in which subject–auxiliary inversion is required.
It also includes the auxiliary do (does, did); this is used with the basic infinitive of other verbs (those not belonging to the "special verbs" class) to make their question and negation forms, as well as emphatic forms (do I like you?; he doesn't speak English; we did close the fridge). For more details of this, see do-support.

Modern English

EnglishModernmodern spoken English
It is not idiomatic in Modern English to add the negating word not to a lexical verb with finite form; not can be added only to an auxiliary or copular verb.
Do-support for the verb "have"

Infinitive

to''-infinitivebare infinitiveinfinitive phrase
Do-support is not used when there is already an auxiliary or copular verb present or with non-finite verb forms (infinitives and participles).
(Periphrases can be employed instead in some cases, like (to) be able to for can, and (to) have to for must.) It also applies to the auxiliary do, like used in questions, negatives and emphasis like described under do-support.

English clause syntax

frontingconditional
English clause syntax
However such inversion is only possible with an auxiliary or copular verb; if no such verb would otherwise be present, do-support is used.

Interrogative

interrogative sentenceinterrogative moodQuestions
The presence of an auxiliary (or copular) verb allows subject–auxiliary inversion to take place, as is required in most interrogative sentences in English.
In sentences where no such verb is otherwise present, the auxiliary do (does, did) is introduced to enable the inversion (for details see do-support, and.

Tag question

tag questionsquestion tagtag-question
Tag questions:
If the verb is in the present perfect, for example, the tag question uses has or have; if the verb is in a present progressive form, the tag is formed with am, are, is; if the verb is in a tense which does not normally use an auxiliary, like the present simple, the auxiliary is taken from the emphatic do form; and if the sentence has a modal auxiliary, this is echoed in the tag:

Negative inversion

The same principles as for question formation apply to other clauses in which subject–auxiliary inversion is required, particularly after negative expressions and expressions involving only (negative inversion):
b. Nothing did Fred say. - Fronted argument; do-support appears to enable subject-auxiliary inversion.

English verbs

English-edEnglish regular verbs
English verbs
Other verbs used as auxiliaries include have, chiefly in perfect constructions (the forms has, have and had can contract to 's, 've and 'd), and do (does, did) in emphatic, inverted and negated constructions (see do-support).

Do

daredoing
The English verb, do, which may serve as an auxiliary verb; see do-support

English auxiliaries and contractions

auxiliary verbcontractedauxiliaries
forms of the verb do (do, does, did), when used with other verbs to enable the formation of questions, negation, emphasis, etc. (see do-support);

Does

English modal verbs

modal verbswouldshall
The verb used in the expression used to (do something) can behave as a modal, but is more often used with do-support than with auxiliary-verb syntax: Did she used to do it? (or Did she use to do it?) and She didn't used to do it (or She didn't use to do it) are more common than Used she to do it? and She used not (usedn't) to do it.

Past tense

pastpast-tensePST
The simple past consists of just the past tense (preterite) form of the verb (he walked, they flew, etc.), although when it is negated, emphasized or inverted it is sometimes necessary to unfuse the verb, using a periphrastic construction with did (as in did he walk? etc.) – see do-support. The simple past is used for describing single occurrences or habitual occurrences in the past, and sometimes for states existing in the past.

Inverted sentence

In English, such an inversion often introduces do-support.

English language

EnglishEnglish-languageen
Some changes, such as the use of do-support have become universalised.

Uses of English verb forms

past progressivesimplefuture-in-the-past
Negation uses do-support (i.e. do not or don't). For example:

Affirmation and negation

negationnegativepolarity
If no such verb is present then the dummy auxiliary do (does, did) is introduced – see do-support.