''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 Negation (linguistics), negated clauses and questions as well as other constructions in which subject–auxiliary inversion is required. The verb "do" can be used as an auxiliary even in simple declarative sentences, and it usually serves to add emphasis, as in "I ''did'' shut the fridge." However, in the negated and inverted clauses referred to above, it is used because the conventions of Modern English syntax permit these constructions only when an auxiliary is present. It is not idiomatic in Modern English to add the negating word ''not'' to a lexical verb with finite verb, finite form; ''not'' can be added only to an auxiliary or copular verb, copular verb. For example, the sentence ''I am not'' with the copula ''be'' is fully idiomatic, but ''I know not'' with a finite lexical verb, while grammatical, is archaism, archaic. If there is no other auxiliary present when negation is required, the auxiliary ''do'' is used to produce a form like ''I do not (don't) know.'' The same applies in clauses requiring inversion, including most questions: inversion must involve the subject and an auxiliary verb so it is not idiomatic to say ''Know you him?''; today's English usually substitutes ''Do you know him?'' ''Do''-support is not used when there is already an auxiliary or copular verb present or with non-finite verb forms (infinitives and participles). It is sometimes used with English subjunctive, subjunctive forms. Furthermore, the use of ''do'' as an auxiliary should be distinguished from the use of ''do'' as a normal lexical verb, as in ''They do their homework''.

Common uses

''Do''-support appears to accommodate a number of varying grammatical constructions: #question formation, #the appearance of the negation ''not'', and #negative inversion. These constructions often cannot occur without ''do''-support or the presence of some other auxiliary verb.

In questions

The presence of an auxiliary (or copular) verb allows subject–auxiliary inversion to take place, as is required in most interrogative sentences in English. If there is already an auxiliary or copula present, ''do''-support is not required when forming questions: :* ''He will laugh.'' → ''Will he laugh?'' (the auxiliary ''will'' inverts with the subject ''he'') :* ''She is at home.'' → ''Is she at home?'' (the copula ''is'' inverts with the subject ''she'') This applies not only in yes–no questions but also in questions formed using interrogative words: :* ''When will he laugh?'' However, if there is no auxiliary or copula present, inversion requires the introduction of an auxiliary in the form of ''do''-support: :* ''I know.'' → ''Do I know?'' (Compare: ''*Know I?'') :* ''He laughs.'' → ''Does he laugh?'' (Compare: ''*Laughs he?'') :* ''She came home.'' → ''Did she come home?'' (Compare: ''*Came she home?'') The finite (inflected) verb is now the auxiliary ''do''; the following verb is a bare infinitive which does not inflect: ''does he laugh?'' (not ''laughs''); ''did she come?'' (not ''came''). In negated questions, the negating word ''not'' may appear either following the subject, or attached to the auxiliary in the contraction (grammar), contracted form ''n't''. That applies both to ''do''-support and to other auxiliaries: :* ''Why are you not playing? / Why aren't you playing?'' :* ''Do you not want to try? / Don't you want to try?'' The above principles do not apply to ''wh''-questions if the interrogative word is the subject (grammar), subject or part of the subject. Then, there is no inversion and so there is no need for ''do''-support: ''Who lives here?'', ''Whose dog bit you?'' The verb ''have'', in the sense of possession, is sometimes used without ''do''-support as if it were an auxiliary, but this is considered dated. The version with ''do''-support is also correct: :* ''Have you any idea what is going on here?'' :* ''Do you have any idea what is going on here?'' :* (''Have you got any idea what is going on here?'' – the order is similar to the first example, but ''have'' is an auxiliary verb here) For elliptical questions and tag questions, see the #In elliptical sentences, elliptical sentences section below.

With ''not''

In the same way that the presence of an auxiliary allows question formation, the appearance of the negating word ''not'' is allowed as well. Then too, if no other auxiliary or copular verb is present, ''do''-support is required. :* ''He will laugh.'' → ''He will not laugh.'' (''not'' attaches to the auxiliary ''will'') :* ''She laughs.'' → ''She does not laugh.'' (''not'' attaches to the added auxiliary ''does'') In the second sentence, ''do''-support is required because idiomatic Modern English does not allow forms like ''*She laughs not''. The verb ''have'', in the sense of possession, is sometimes negated thus: :* ''I haven't the foggiest idea.'' Most combinations of auxiliary/copula plus ''not'' have a contraction (grammar), contracted form ending in suffix ''-n't'', such as ''isn't'', ''won't'', etc. The relevant contractions for negations formed using ''do''-support are ''don't'', ''doesn't'' and ''didn't''. Such forms are used very frequently in informal English. ''Do''-support is required for negated imperative mood, imperatives even when the verb is the copula ''be'': :*''Do not do that.'' :*''Don't be silly.'' However, there is no ''do''-support with non-finite, as they are negated by a preceding ''not'': :*''It would be a crime not to help him'' (the infinitive ''to help'' is negated) :*''Not knowing what else to do, I stood my ground'' (the present participle ''knowing'' is negated) :*''Not eating vegetables can harm your health'' (the gerund ''eating'' is negated) With English subjunctive, subjunctive verb forms, as a present subjunctive, ''do'' is infrequently used for negation, which is frequently considered ambiguous or incorrect because it resembles the indicative. The usual method to negate the present subjunctive is to precede the verb with a ''not'', especially if the verb is ''be'' (as ''do''-support with it, whether it be indicative or subjunctive, is ungrammatical): :*''I suggest that he not receive any more funding'' (the present subjunctive ''receive'' is negated) :*''It is important that he not be there'' (the present subjunctive ''be'' is negated) As a past subjunctive, however, ''did'' is needed for negation (unless the verb is ''be'', whose past subjunctive is ''were''): :*''I wish that he did not know it'' :*''I wish that he were not here'' The negation in the examples negates the non-finite predicate (grammar), predicate. Compare the following competing formulations: :*''I did not try to laugh.'' vs. ''I tried not to laugh''. :*''They do not want to go.'' vs. ''They want not to go''. There are two predicates in each of the verb chains in the sentences. ''Do''-support is needed when the higher of the two is negated; it is not needed to negate the lower nonfinite predicate. For negated questions, see the #In questions, questions section above. For negated ellipsis (linguistics), elliptical sentences, see the #In elliptical sentences, elliptical sentences section below.

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): :* ''Never did he run that fast again.'' (wrong: ''*Never he did run that fast again. *Never ran he that fast again.'') :* ''Only here do I feel at home.'' (wrong: ''*Only here feel I at home.'')

Further uses

In addition to providing ''do''-support in questions and negated clauses as described above, the auxiliary verb ''do'' can also be used in clauses that do not require ''do''-support. In such cases, ''do''-support may appear for pragmatic reasons.

For emphasis

The auxiliary generally appears for purposes of emphasis, for instance to establish a contrast or to express a correction: :* ''Did Bill eat his breakfast? Yes, he did eat his breakfast'' (''did'' emphasizes the positive answer, which may be unexpected). :* ''Bill doesn't sing, then. No, he does sing'' (''does'' emphasizes the correction of the previous statement). As before, the main verb following the auxiliary becomes a bare infinitive, which is not inflected (one cannot say *''did ate'' or *''does sings'' in the above examples). As with typical ''do''-support, that usage of ''do'' does not occur with other auxiliaries or a copular verb. Then, emphasis can be obtained by adding stress (linguistics), stress to the auxiliary or copular: :* ''Would you take the risk? Yes, I would take the risk.'' :* ''Bill isn't singing, then. No, he is singing.'' (Some auxiliaries, such as ''can'', change their pronunciation when stressed; see Weak and strong forms in English.) In negative sentences, emphasis can be obtained by adding stress either to the negating word (if used in full) or to the contracted form ending in ''n't''. That applies whether or not ''do''-support is used: :* ''I wouldn't'' (or ''would not'') ''take the risk.'' :* ''They don't'' (or ''do not'') ''appear on the list.'' Emphatic ''do'' can also be used with imperatives, including with the copula ''be'': :* ''Do take care! Do be careful!''

In elliptical sentences

The auxiliary ''do'' is also used in various types of ellipsis (linguistics), elliptical sentences, where the main verb is omitted (it can be said to be "understood", usually because it would be the same verb as was used in a preceding sentence or clause). That includes the following types: *Tag questions: ** ''He plays well, doesn't he?'' ** ''You don't like Sara, do you?'' *Elliptical questions: ** ''I like pasta. Do you?'' ** ''I went to the party. Why didn't you?'' *Elliptical statements: ** ''They swam, but I didn't.'' ** ''He looks smart, and so do you.'' ** ''You fell asleep, and I did, too.'' Such uses include cases that ''do''-support would have been used in a complete clause (questions, negatives, inversion) but also cases that (as in the last example) the complete clause would normally have been constructed without ''do'' (''I fell asleep too''). In such instances ''do'' may be said to be acting as a pro-verb since it effectively takes the place of a verb or verb phrase: ''did'' substitutes for ''fell asleep''. As in the principal cases of ''do''-support, ''do'' does not normally occur when there is already an auxiliary or copula present; the auxiliary or copula is retained in the elliptical sentence: :*''He is playing well, isn't he?'' :*''I can cook pasta. Can you?'' :*''You should get some sleep, and I should too.'' However, it is possible to use ''do'' as a pro-verb (see below section #Pro-verbs & Do-so Substitution even after auxiliaries in some dialects: *''Have you put the shelf up yet? I haven't done'' (or ''I haven't'')'', but I will do'' (or ''I will''). (However it is not normally used in this way as a ''to''-infinitive: ''Have you put the shelf up? I plan to'', rather than *''I plan to do''; or as a passive voice, passive participle: ''Was it built? Yes, it was'', not *''Yes, it was done''.) Pro-verbal uses of ''do'' are also found in the imperative: ''Please do. Don't!''

Pro-verbs and do-so substitution

The phrases ''do so'' and ''do what'' for questions are pro-verb forms in English. They can be used as substitutes for verbs in x-bar theory grammar to test verb phrase completeness. Bare infinitives forms often are used in place of the missing pro-verb#in English, pro-verb forms. Examples from Santorini and Kroch:

Tests for constituenthood of a verb-phrase in X'-grammar

The ''do so'' construction can be used to test if a verb-phrase is a constituent phrase in X'-grammar by substitution similarly to how other pro-forms can be used to test for noun-phrases, etc. In X-bar theory, the verb-phrase projects three bar-levels such as this:

    VP
   / \
 ZP  X'
     / \
    X'  YP
    , 
    X 
    , 
   head

With a simple sentence:

         S
         , 
         VP
        /  \
       /    \
      /      \
     /        \
    NP         \
   /  \         \   
 DP    N'        V'
 ,      ,         / \
The  children  /   \
              /     \
              V'     PP
             /  \   /_\
            /    \  with gusto
           V     NP
           ,      /_\
          ate  the pizza

Here again exemplified by Santorini and Kroch, ''do so'' substitution for testing constituent verb phrases in the above sample sentence:

         S
         , 
         VP
        /  \
       /    \
      /      \
     /        \
    NP         \
   /  \         \   
 DP    N'        V'
 ,      ,         / \
The  children  /   \
              /     \
              V'     PP
             /  \   /_\
            /    \  with gusto
           V     NP
           ,      /_\
        did so   the pizza

Use of ''do'' as main verb

Apart from its uses as an auxiliary, the verb ''do'' (with its inflected forms ''does'', ''did'', ''done'', ''doing'') can be used as an ordinary lexical verb (main verb): :*''Do your homework!'' :*''What are you doing?'' Like other non-auxiliary verbs, ''do'' cannot be directly negated with ''not'' and cannot participate in inversion so it may itself require ''do''-support, with both auxiliary and lexical instances of ''do'' appearing together: :* ''They didn't do the laundry on Sunday.'' (''did'' is the auxiliary, ''do'' is the main verb) :* ''Why do you do karate?'' (the first ''do'' is the auxiliary, the second is the main verb) :* ''How do you do?'' (a set phrase used as a polite greeting)

Meaning contribution

In the various cases seen above that require ''do''-support, the auxiliary verb ''do'' makes no apparent contribution to the meaning of the sentence so it is sometimes called a dummy auxiliary. Historically, however, in Middle English, auxiliary ''do'' apparently had a meaning contribution, serving as a marker of grammatical aspect, aspect (probably perfective aspect, but in some cases, the meaning may have been imperfective). In Early Modern English, the semantic value was lost, and the usage of forms with ''do'' began to approximate that found today.

Origins

Some form of auxiliary "do" occurs in all West Germanic languages except Afrikaans. It is generally accepted that the past tense of Germanic weak verbs (in English, -ed) was formed from a combination of the infinitive with a past tense form of "do", as exemplified in Gothic language, Gothic. The origins of the construction in English are debated: some scholars argue it was already present in Old English, but not written due to stigmatization. Scholars disagree whether the construction arose from the use of "do" as a lexical verb in its own right, or whether periphrastic "do" arose from a causative meaning of the verb or vice versa. Examples of auxiliary "do" in Old English writing appear to be limited to its use in a causative sense, which is parallel to the earliest uses in other West Germanic languages. Some scholars, such as linguist John McWhorter, argue that the construction arose via Brittonicisms in English#Transition to Middle English, the influence of Celtic speakers. Others contend that the construction arose as a form of creolization when native speakers addressed foreigners and children.

References

{{reflist English grammar Word order Syntax Generative syntax