Subject–auxiliary inversion

Subject–auxiliary inversion involves placing the subject after a finite auxiliary verb,[2] rather than before it as is the case in typical declarative sentences (the canonical word order of English being subject–verb–object). The auxiliary verbs which may participate in such inversion (e.g. is, can, have, will, etc.) are described at English auxiliaries and contractions. Note that forms of the verb be are included regardless of whether or not they function as auxiliaries in the sense of governing another verb form. (For exceptions to this restriction, see § Inversion with other types of verb below.)

A typical example of subject–auxiliary inversion is given below.

a. Sam has read the paper. - Statement

b. Has Sam read the paper? - Yes–no question formed using inversion

Here the subject is Sam, and the verb has is an auxiliary. In the question, these two elements change places (invert). If the sentence does not have an auxiliary verb, this type of simple inversion is not possible. Instead, an auxiliary must be introduced into the sentence in order to allow inversion:[3]

a. Sam enjoys the paper. - Statement with the non-auxiliary verb enjoys

b. *Enjoys Sam the paper? - This is idiomatically incorrect; simple inversion with this type of verb is considered archaic

c. Sam does enjoy the paper. - Sentence formulated with the auxilary verb does

d. Does Sam enjoy the paper? - The sentence formulated with the auxiliary does now allows inversion

For details of the use of do, did and does for this and similar purposes, see do-support. For exceptions to the principle that the inverted verb must be an auxiliary, see § Inversion with other types of verb below. It is also possible for the subject to invert with a negative contraction (can't, isn't, etc.). For example:

a. He isn't nice.

b. Isn't he nice? - The subject he inverts with the negated auxiliary contraction isn't

Compare this with the uncontracted form Is he not nice? and the archaic Is not he nice?.

The main uses of subject–auxiliary inversion in English are described in the following sections, although other types can occasionally be found.[4] Most of these uses of inversion are restricted to main clauses; they are not found in subordinate clauses. However other types (such as inversion in condition clauses) are specific to subordinate clauses.

There are certain sentence patterns in English in which subject–verb inversion takes place where the verb is not restricted to an auxiliary verb. Here the subject may invert with certain main verbs, e.g. After the pleasure comes the pain, or with a chain of verbs, e.g. In the box will be a bottle. These are described in the article on subject-verb inversion. Further, inversion was not limited to auxiliaries in older forms of English. Examples of non-auxiliary verbs being used in typical subject–auxiliary inversion patterns may be found in older texts or in English written in an archaic style:

Know you what it is to be a child? (Francis Thompson)

The verb have, when used to denote broadly defined possession (and hence not as an auxiliary), is still sometimes used in this way in modern standard English:

Have you any idea what this would cost?

In some cases of subject–auxiliary inversion, such as negative inversion, the effect is to put the finite auxiliary verb into second position in the sentence. 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.). These instances of inversion are remnants of the V2 pattern that formerly existed in English as it still does in its related languages. Old English followed a consistent V2 word order.

Syntactic theories based on phrase structure typically analyze subject-aux inversion using syntactic movement. In such theories, a sentence with subject-aux inversion has an underlying structure where the auxiliary is embedded deeper in the structure. When the movement rule applies, it moves the auxiliary to the beginning of the sentence.[5]

An alternative analysis does not acknowledge the binary division of the clause into subject NP and predicate VP, but rather it places the finite verb as the root of the entire sentence and views the subject as switching to the other side of the finite verb. No discontinuity is perceived. Dependency grammars are likely to pursue this sort of analysis.[6] The following dependency trees illustrate how this alternative account can be understood:

These trees show the finite verb as the root of all sentence structure. The hierarchy of words remains the same across the a- and b-trees. If movement occurs at all, it occurs rightward (not leftward); the subject moves rightward to appear as a post-dependent of its head, which is the finite auxiliary verb.