Subject–auxiliary inversionwikipedia
Subject–auxiliary inversion (also called subject–operator inversion) is a frequently occurring type of inversion in English, whereby a finite auxiliary verb – taken here to include finite forms of the copula be – appears to "invert" (change places) with the subject.
subject–auxiliary inversionsubject-auxiliary inversioninversioninversion of subject and auxiliaryinvert

Inversion (linguistics)

inversioninvertedinverting
Subject–auxiliary inversion (also called subject–operator inversion) is a frequently occurring type of inversion in English, whereby a finite auxiliary verb – taken here to include finite forms of the copula be – appears to "invert" (change places) with the subject.
The most frequent type of inversion in English is subject–auxiliary inversion in which an auxiliary verb changes places with its subject; it often occurs in questions, such as Are you coming?, with the subject you is switched with the auxiliary are.

Negative inversion

negative inversion
The most frequent use of subject–auxiliary inversion in English is in the formation of questions, although it also has other uses, including the formation of condition clauses, and in the syntax of sentences beginning with negative expressions (negative inversion).
In linguistics, negative inversion is one of many types of subject-auxiliary inversion in English.

English auxiliaries and contractions

auxiliary verbcontractedauxiliaries
The auxiliary verbs which may participate in such inversion (e.g. is, can, have, will, etc.) are described at English auxiliaries and contractions.
In English, verbs are often classed as auxiliaries on the basis of certain grammatical properties, particularly as regards their syntax – primarily whether they participate in subject–auxiliary inversion, and can be negated by the simple addition of not after them.

Copula (linguistics)

copulato becopular
Subject–auxiliary inversion (also called subject–operator inversion) is a frequently occurring type of inversion in English, whereby a finite auxiliary verb – taken here to include finite forms of the copula be – appears to "invert" (change places) with the subject.

Do-support

do''-supportdo-supportinserted
For details of the use of do, did and does for this and similar purposes, see do-support.
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.

Subject–verb inversion in English

locative inversionsubject-verb inversionsubject–verb inversion
In certain types of English sentences, inversion is also possible with verbs other than auxiliaries; these are described in the article on subject-verb inversion.
Subject–verb inversion is distinct from subject–auxiliary inversion because the verb involved is not an auxiliary verb.

English language

EnglishEnglish-languageen
Subject–auxiliary inversion (also called subject–operator inversion) is a frequently occurring type of inversion in English, whereby a finite auxiliary verb – taken here to include finite forms of the copula be – appears to "invert" (change places) with the subject.
Questions are marked by do-support, wh-movement (fronting of question words beginning with wh-) and word order inversion with some verbs.

Auxiliary verb

auxiliary verbauxiliaryauxiliary verbs
Subject–auxiliary inversion (also called subject–operator inversion) is a frequently occurring type of inversion in English, whereby a finite auxiliary verb – taken here to include finite forms of the copula be – appears to "invert" (change places) with the subject.
The verbs listed in the previous section can be classified as auxiliaries based upon two diagnostics: they allow subject–auxiliary inversion (the type of inversion used to form questions etc.) and (equivalently) they can take not as a postdependent (a dependent that follows its head).

Subject (grammar)

subjectsubjectsgrammatical subject
Subject–auxiliary inversion (also called subject–operator inversion) is a frequently occurring type of inversion in English, whereby a finite auxiliary verb – taken here to include finite forms of the copula be – appears to "invert" (change places) with the subject.
In the second sentence, which involves the subject-auxiliary inversion of a yes/no-question, the subject immediately follows the finite verb (instead of immediately preceding it), which means the second criterion is flouted.

Wh-movement

wh-movementwh''-frontingwh-fronting
In this case the subject remains before the verb (it can be said that wh-fronting takes precedence over subject–auxiliary inversion):
Wh-fronting in main clauses is often reliant on subject-auxiliary inversion.

Penthouse principle

penthouse principle
Inversion also does not normally occur in indirect questions, where the question is no longer in the main clause, due to the penthouse principle.
Perhaps the best-known example of a penthouse principle effect is the distribution of subject-auxiliary inversion in constituent questions in English, which in many (but not all) varieties of English is restricted to matrix clauses:

V2 word order

verb-secondV2verb-second word order
In these cases, inversion in English results in word order that is like the V2 word order of other Germanic languages (Danish, Dutch, Frisian, Icelandic, German, Norwegian, Swedish, Yiddish, etc.).
Interrogative Wh- questions (like Yes/No questions) are regularly formed with inversion of subject and auxiliary.

Contraction (grammar)

contractioncontractionscontracted
In subject–auxiliary inversion, the contracted negative forms behave as if they were auxiliaries themselves, changing place with the subject.

English modal verbs

modal verbsshalldouble modal
Again like other auxiliaries, modal verbs undergo inversion with their subject, in forming questions and in the other cases described in the article on subject–auxiliary inversion: Could you do this?; On no account may you enter. When there is negation, the contraction with n't may undergo inversion as an auxiliary in its own right: Why can't I come in? (or: Why can I not come in?).

English conditional sentences

first conditionalsecond conditional
Certain condition clauses can also be formulated using inversion without any conjunction; see below.

Clause

clauseclausesfinite clause
They express a yes/no-question via subject–auxiliary inversion, 2.

Conditional sentence

conditional sentenceprotasisapodosis
Certain condition clauses can also be formulated using inversion without any conjunction (should you fail...; were he to die...; had they helped us... ; see also the corresponding section about inversion in the English subjunctive article).

Syntactic movement

movementtracesyntactic movement
An analysis of subject-auxiliary inversion that acknowledges rightward movement can dispense with head movement entirely, e.g.

Uses of English verb forms

past progressivesimplefuture-in-the-past
Questions (interrogative constructions) are generally formed using subject–auxiliary inversion, again using do-support if there is otherwise no auxiliary.

English clause syntax

frontingconditional
For details see subject–auxiliary inversion and negative inversion.

Simple past

simple pastpast simplesimple past tense
Questions, other clauses requiring inversion, negations with not, and emphatic forms of the simple past use the auxiliary did.

English subjunctive

subjunctivesubjunctive moodpast subjunctive
As noted in the sections above, some clauses containing subjunctive verb forms, or other constructions that have the function of subjunctives, may exhibit subject–auxiliary inversion (an auxiliary or copular verb changes places with the subject of the clause).