Modals and auxiliary verbs in English (2023)

Modals and auxiliary verbs in English

  • Modals
  • Auxiliary do
  • Auxiliary have
  • Be (auxiliary and main verb)
  • Summary
  • Notes


Historically, the modals of English, which are listed in (1), derivefrom a special class of verbs in Germanic (the ancestor of English and theother Germanic languages).

(1)can, could, may, might, must, shall, should, will, would

Modals have always differed from ordinary verbs in Germanic, and inthe course of the history of English, they have diverged from verbs evenfurther, to the point where they now belong to a syntactic category oftheir own. Because many modals have meanings that are often expressedin other languages by verbal inflections, this syntactic category iscalled I(nflection).

In what follows, we review the ways that modals differ from verbs inEnglish, both morphologically (what forms they exhibit) and syntactically(how they combine in sentences).

Range of forms

Modals and verbs differ in the range of forms that they exhibit.English verbs appear in a number of distinct forms (see Finiteness),whereas modals have a single, invariant form. Modals never end in-s, even in sentences with third person singular subjects.

(2)a.*She { can-s, may-s } play the piano.
b.She { can, may } play the piano.

Modals also lack productive past tense forms. It is true thatcould, might, should, and would originatedin Germanic as past tense forms of can, may, shall,and will. But today, only could can serve as the pasttense of can, and that only in certain contexts.1

ExamplePotential paraphrase
(3)a.Nowadays, you can get one for a dollar.=... it is possible to get one ...
b.Back then, you could get one for a nickel.=... it was possible to get one ...
(4)a.We can go there tomorrow.=It is possible for us to go there ...
b.We could go there tomorrow.=/=It was possible for us to go there ...
(5)a.You may ask the boss.=You are allowed to ask the boss.
b.You might ask the boss.=/=You were allowed to ask the boss.
(6)a.Shall I pick up some bread?=Is it a good idea for me to pick up some bread?
b.Should I pick up some bread?=/=Was it a good idea for me to pick up some bread?

Finally, modals lack present and past participles; the missing forms must beparaphrased.

(7)a.*{ Cann-ing, may-ing } play the piano pleases her greatly.
b.{ Being able, being allowed } to play the piano pleases her greatly.
(8)a.*She has { cann-ed, may-ed } play the piano.
b.She has { been able, been allowed } to play the piano.

Nonfinite contexts

A further difference between modals and verbs is that modals, unlikeverbs, can't occur in nonfinite contexts (for instance, in toinfinitive clauses or after another modals). Once again, the missingforms must be paraphrased.

(9)a.In to infinitive clause,modal*She wantsto can speak Spanish.
b.paraphrase of modalShe wantsto be able to speak Spanish.
c.verbShe wantsto speak Spanish.
(10)a.After (another) modal,modal*She mustcan speak Spanish.
b.paraphrase of modalShe mustbe able to speak Spanish.
c.verbShe mustspeak Spanish.

Do support contexts

The inability of modals to appear in nonfinite contexts gives riseto three further differences between verbs and modals, all of themmanifestations of an important phenomenon in the grammar of Englishcalled do support.

Emphasis.In the simplest case, do support affects affirmative sentencescontaining a finite verb whose truth is being emphasized. It involvesreplacing the finite verb by the verb's bare form and adding a form ofauxiliary do to the sentence inthe appropriate tense (either present or past tense). This form ofdo then receives emphatic stress, as indicated by underlining in(11).

(11)a.Unemphatic (without do support)He dances; she sang.
b.Emphatic (with do support)He does dance; she did sing.

By contrast, emphasizing the truth of a sentence that contains a modalis achieved by simply stressing the modal. Do support with modalsis ungrammatical.

(12)a.Emphasis without do supportHe can dance; she will sing.
b.Emphasis with do support*He does can dance; she does will sing.

Negation.Do support with verbs occurs not only in emphatic contexts, butin two further syntactic contexts: negation and question formation. In both ofthese cases, the form of do that is added to the affirmative ordeclarative sentence doesn't necessarily receive emphatic stress(although it can).

In English, sentences containing modals are negated by simply addingnot (or its contracted form n't) after the modal. Dosupport is ungrammatical.

(13)a.Negation without do supportHe { may, must, should, will, would } not dance.
b.Negation with do support*He does not { may, must, should, will, would } dance.

Sentences without modals, on the other hand, require dosupport in English. As in the case of emphasis, the verb appears in itsbare form, and an appropriately tensed form of the auxiliary verbdo is added to the sentence, followed by negation.

(14)a.Negation with do supportHe { does, did } not dance.
b.Negation without do support*He not { dances, danced }.
He { dances, danced } not.

Question formation.The final difference between modals and verbs concerns questionformation. If a declarative sentence contains a modal, thecorresponding question is formed by inverting the modal with thesubject. Do support is ungrammatical.

(15)a.Question without do support{ Can, may, must, should, will, would } he dance?
b.Question with do support*Does he { can, may, must, should, will, would } dance?

Again, however, in a sentence without a modal, question formationrequires do support. That is, it is an appropriately tensed formof do, rather than the verb itself, that inverts with thesubject.

(16)a.Question with do support{ Does, Did } he dance?
b.Question without do support*{ Dances, Danced } he?

Auxiliary do

This section summarizes the properties of auxiliary do,introduced in the previoussection in connection with do support. Auxiliary dobelongs to the same syntactic category as the modals---namely,I(nflection), because it shares their properties with one exception (incontrast to modals, it has an -s form).

The goal of the previoussection was to establish the special status of modals, and we usedthe facts of do support as a criterion for distinguishing modalsfrom verbs. In this section, we consider some of the same facts, butwith a different focus. Rather than focusing on the distinctiveproperties of modals, we focus on the morphological and syntacticproperties of auxiliary do itself.

Like all English auxiliaries (the others are be andhave), auxiliary do is homonymous with an ordinaryverb - in this case, main verb do. The examples that followexplicitly contrast main verb do with auxiliary do.

Range of forms

As just mentioned, the only difference between auxiliary do andthe modals is that it has an -s form. In this respect, itpatterns with ordinary verbs, including its main verb counterpart.
(17)a.ModalI can dance the polka.
b.He { can, * can-s } dance the polka.
(18)a.Auxiliary doI do dance the polka; I do not dance the polka; do you dance the polka?
b.He do-es dance the polka; he do-es not dance the polka; do-es he dance the polka?
(19)a.Main verb doI do the dishes.
b.He do-es the dishes.
(20)a.Other verbI dance the polka.
b.He dance-s the polka.

Nonfinite contexts

In all other respects, auxiliary do behaves like a modalrather than like an ordinary verb. For instance, it is ungrammatical asa to infinitive, after modals, or as a gerund. Notice the clearcontrast between the judgments for auxiliary do in (22) and mainverb do in (23).

(21)a.Modal,in to infinitive*They want to can dance the polka.
b.after (another) modal*They will can dance the polka.
c.gerund*Their canning dance the polka while blindfolded is unusual.
(22)a.Auxiliary do,in to infinitive*They claim to do dance the polka.
Intended meaning: They claim that they do dance the polka.
b.after modal*They will do dance the polka.
Intended meaning: It will be the case they do dance the polka.
c.gerund*Their doing dance the polka while blindfolded was unwise.
Intended meaning: That they did dance the polka while blindfolded was unwise.
(23)a.Main verb do,in to infinitiveThey want to do the dishes.
b.after modalThey will do the dishes.
c.gerundTheir doing the dishes was considerate.
(24)a.Other verb,in to infinitiveThey want to dance the polka.
b.after modalThey will dance the polka.
c.gerundTheir dancing the polka while blindfolded is unwise.

Do support contexts

Auxiliary do also behaves like a modal in do supportcontexts. Double instances of auxiliary do are ruled out, justlike double modals are (see (10a)). Once again, auxiliary do andmain verb do differ sharply, as shown in (26) and (27).

(25)a.Modal,after emphatic do*He does can dance the polka.
b.negative*He doesn't can dance the polka.
c.question*Does he can dance the polka?
(26)a.Auxiliary do,after emphatic do*He does do dance the polka.
Intended meaning: It is the case that he does dance the polka.
b.negative*He doesn't do dance the polka.
Intended meaning: It isn't the case that he does dance the polka.
c.question*Doesn't he do dance the polka?
Intended meaning: Isn't it the case that he does dance the polka?
(27)a.Main verb do,after emphatic doHe does do the dishes.
b.negativeHe doesn't do the dishes.
c.questionDoes he do the dishes?
(28)a.Other verb,after emphatic doHe does dance the polka.
b.negativeHe doesn't dance the polka.
c.questionDoes he dance the polka?

Auxiliary have

Let's now turn to auxiliary have, which combines with pastparticiples (-en forms) to form the perfect forms ofverbs. Auxiliary have behaves like a V with respect to itsmorphology and its occurrence in nonfinite contexts, but like an I withrespect to do support. Specifically, auxiliary have, likeauxiliary do, shares all the morphological properties of its mainverb counterpart. In addition, it can appear in nonfinite contexts(unlike auxiliary do). With respect to do support,however, auxiliary have differs from its main verb counterpartand patterns together with the modals and auxiliary do. Thecomplex behavior of auxiliary have can be captured by saying thatit moves from V to I in the derivation of a sentence (see Chapter 6 for detaileddiscussion of V-to-I movement).

(29) and (30) show that auxiliary have, like auxiliary do(cf. (18)), behaves morphologically like its main verb counterpart inhaving an -s form.

(29)a.Auxiliary haveI have adopted two cats.
b.She ha-s adopted two cats.
(30)a.Main verb haveI have two cats.
b.She ha-s two cats.

Auxiliary have differs from auxiliary do (cf. (22))and resembles main verb have in being able to appear in nonfinitecontexts.

(31)a.Auxiliary have,to infinitiveThey claim to have adopted two cats.
b.after modalThey must have adopted two cats.
c.gerundI do not regret having adopted two cats.
(32)a.Main verb have,to infinitiveThey claim to have two cats.
b.after modalThey must have two cats.
c.gerundI do not regret having two cats.

On the other hand, just like auxiliary do (cf. (26)) and incontrast to main verb have, auxiliary have is ruled out indo support contexts.

(33)a.Auxiliary have,after emphatic do*He does have adopted two cats.
b.negative*He doesn't have adopted two cats.
c.question*Does he have adopted two cats?
(34)a.Main verb have,after emphatic doHe does have two cats.
b.negativeHe doesn't have two cats.
c.questionDoes he have two cats?

Be (auxiliary and main verb)

The examples in (35)-(40) illustrate the behavior of auxiliarybe, which is used to form the progressive (is coming, wasdancing) and the passive (is abandoned, was sold) in English.Auxiliary be behaves just like auxiliary have. Inparticular, it has an -s form (irregular though that form is),and it can appear in nonfinite contexts, but it is excluded fromdo support contexts. As a result, auxiliary be can betreated just like auxiliary have: as belonging to the syntacticcategory V, but moving from V to I in the course of a derivation.

Main verb be differs from main verb have and main verbdo in behaving exactly like auxiliary be. In other words,main verb be is the only main verb in modern English that movesfrom V to I.

(35)a.Auxiliary be,non-third personI am learning Spanish; I am invited to the ceremony.
b.third personShe i-s learning Spanish; she i-s invited to the ceremony.
(36)a.Main verb be,non-third personI am happy.
b.third personShe i-s happy.
(37)a.Auxiliary be,to infinitiveThey claim to be learning Spanish; they claim to be invited to the ceremony.
b.after modalThey must be learning Spanish; they must be invited to the ceremony.
c.gerund2I don't regret being invited to the ceremony.
(38)a.Main verb be,to infinitiveThey claim to be happy.
b.after modalThey must be happy.
(39)a.Auxiliary be,after emphatic do*She does be learning Spanish; she does be invited to the ceremony.
b.negative*She doesn't be learning Spanish; she doesn't be invited to the ceremony.
c.question*Does she be learning Spanish? Does she be invited to the ceremony?
(40)a.Main verb be,after emphatic do*She does be happy.
b.negative*She doesn't be happy.
c.question*Does she be happy?


The table in (41) provides a synopsis of the morphological andsyntactic properties of the items discussed here, arranged from most toleast verb-like. As is evident from the table, the syntactic categoryof an item depends on whether it is the verb-like or the modal-likeproperties that predominate.

(41)Ordinary verbBe and auxiliary haveAuxiliary doModal
Has -s formyesyesyesno
Occurs in nonfinite contextsyesyesnono
Occurs with do supportyesnonono
Syntactic categoryVVII


1. More precisely, we mustdistinguish between form (morphology) and meaning (reference).Ordinarily, forms with past-tense morphology are used to refer to anevent or state prior to the time of speaking. However, it is possiblein English to use past-tense forms to refer to events or statecontemporaneous with a reported time of speaking; this is the so-calledsequence-of-tense phenomenon in reported speech, illustrated in (i).
(i)a.Direct speech:She said, "They make too much noise."
b.Reported speech:She said that they made too much noise.

As is evident from (ii) and (iii), can, may,shall, and will continue to maintain a productivemorphological relationship with could, might,should, and would, respectively, in sequence-of-tensecontexts.

(ii)a.Direct speech:She said, "That may be so."
b.He told us, "You won't last long."
(iii)a.Reported speech:She said that might be so.
b.He told us that we wouldn't last long.

Nevertheless, in keeping with the point made in the body of thetext, the morphological relationship between the modals in (ii) andtheir counterparts in (iii) is purely formal, lacking the referentialunderpinning evident in (iv).

(iv)a.They make too much noise.
b.They made too much noise.

We thank Aaron Dinkin for drawing our attention to thesequence-of-tense phenomenon.

2. For reasons not wellunderstood, gerunds of progressive forms, as in (i), are unacceptable.

(i)*I like be-ing learn-ing Spanish.
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