English modal auxiliary verbs

The English modal auxiliary verbs are a subset of the English auxiliary verbs used mostly to express modality, properties such as possibility and obligation. They can most easily be distinguished from other verbs by their defectiveness and by their lack of the ending s for the third-person singular.
The central English modal auxiliary verbs are can, may, shall, will, and [|must]. A few other verbs are usually also classed as modals: ought, and dare, and need. Use is included as well. Other expressions, notably had better, share some of their characteristics.

Modal auxiliary verbs distinguished grammatically

A list of what tend to be regarded as modal auxiliary verbs in Modern English, along with their inflected forms, is shown in the following table.
Contractions are shown only if their orthography is distinctive. There are also unstressed versions that are typically, although not necessarily, written in the standard way. Where there is a blank, the modal auxiliary verb lacks this form.

Criteria for modal auxiliary verbs

Descriptive grammars of English differ slightly on the criteria they set for modal auxiliary verbs. According to The Cambridge Grammar of the English Language, the criteria are as follows.

Auxiliary verbs

Modal auxiliary verbs are a subset of auxiliary verbs and thus meet the criteria for these. For lists of those criteria, see the article English auxiliary verbs, but among them are that the verbs can invert with their subjects, can be negated with not, and have negative inflected forms.

No untensed forms

To illustrate untensed forms, those of the irregular lexical verb take and the non-modal auxiliary verb be are the plain take and be, the gerund-participles taking and being, and the past participles taken and been.
Modal auxiliary verbs lack untensed forms. Attempting to use them brings ungrammatical results:

I will can drive if I take ten lessons.
Canning drive would be helpful.
I have could/canned drive since I was 18.

Compare the grammaticality of non-modal auxiliary verb be in I will be able to drive, being able to drive, and I have been able to drive.

No subject–verb agreement

This refers to agreement of a verb with its third-person singular subject:

She can/*cans try.

Compare lexical verb try in She tries/*try, and non-modal auxiliary verb do in She does/*do try.
Had better and used lack present tense forms. Other than in the present tense, even lexical verbs lack subject agreement and so this test is inapplicable to either had better or used.

Only a bare infinitival clause as complement

Whereas the lexical verb seem takes a to-infinitival clause, and the non-modal auxiliary verb have takes a past participial clause complement, a modal auxiliary verb can, in principle, take only a bare infinitival clause as its complement:

It can be a surprise.
It can to be a surprise.
It can being a surprise.

If they are modal auxiliary verbs, then ought and used are exceptions to this.
Bare infinitival clause complements are not unique to modal auxiliary verbs. Do is a non-modal auxiliary verb that takes one ; help is a lexical verb that can do so.

Ability to occur in remote apodosis

An apodosis is the "then" half of a conditional statement. Remote here means "thought by the speaker to be unlikely" or "known by the speaker to be untrue".

If I were an elephant, I would eat more apples.

Compare lexical verb eat in *If I were an elephant, I ate more apples, and non-modal auxiliary verb be in *If I were an elephant, I was able to eat more apples.
Must satisfies this only for a minority of speakers, and it is questionable whether had better does so.
The Cambridge Grammar comments on may that:

here there is evidence that for some speakers may and might have diverged to the extent that they are no longer inflectional forms of a single lexeme, but belong to distinct lexemes, may and might, each of which – like must – lacks a preterite....

Used does not satisfy this.

Preterite usable in the main clause for modal remoteness

I could drive there, I suppose.

If similarly intended, attempts at this with a lexical or non-modal auxiliary verb are ungrammatical: *I drove there, I suppose; *I was going to drive there, I suppose.
Other than when used for backshift, should has diverged in meaning so far from shall as to be usable here only with difficulty. As they lack preterite forms, must, ought and need cannot be used in this way, and so that criterion does not apply to them. And used describes the past, not the present or future.

Comments

The following verbs, shown in present–preterite pairs, satisfy or come close to satisfying all of the above criteria and can be classed as the central modal verbs of English:

can
will
may – although the lack in today's Standard English of a negative present inflection means that it fails one of the criteria for auxiliary verbs
shall – although the semantic divergence of shall and should means that its success with one criterion is debatable
must – although its lack of a preterite means that it neither passes nor fails one of the criteria

Even for lexical verbs, preterite forms have uses besides referring to the past, but for modal auxiliary verbs, such uses are particularly important:.
Ought, dare, need, and used satisfy some of the criteria [|above], and are more or less often categorized as modal verbs. Had better is sometimes called a modal idiom.
Other English auxiliary verbs appear in a variety of different forms and are not regarded as modal verbs:

be, used as an auxiliary verb in passive voice, continuous aspect and indeed in virtually all of its uses, even as a copula;
have, used as an auxiliary verb in perfect aspect constructions and the idiom have got ; it is also used in have to, which has modal meaning, but here have only rarely follows auxiliary verb syntax;
do, see do-support;
to, of to-infinitival clauses.

Lists of modal auxiliary verbs

Five recent scholarly descriptions of verbs disagree among themselves on the extension of modal auxiliary verb: on which verbs are modal auxiliary verbs.
They agree that can, may, must, shall and will are, or are among, the "central modal auxiliaries", "secondary or modal auxiliaries", "modal auxiliaries", "central members of the modal auxiliary class", or "core modal verbs".
Among these five verbs, The Cambridge Grammar selects the pair can and will as "the most straightforward of the modal auxiliaries". Peter Collins agrees.
All five accord ought, need and dare a less clear or merely a marginal membership.
A Comprehensive Grammar and Warner do likewise for use; the other three deny that it is a modal auxiliary verb. For that reason, it is discussed primarily not in this article but in English auxiliary verbs.)
As for would in would rather, would sooner and would as soon, and have in had better, had best and had rather, only The Cambridge Grammar notes all six, but each of the other four descriptions of auxiliary verbs notes three or more. Of the three to six idioms that each discussion notes, there is no variation in the status that it accords to them. Warner calls the three that he notes modal auxiliaries. Palmer says that the same three are not modal auxiliaries. Both A Comprehensive Grammar and Aarts use the term modal idiom for a choice of five. The Cambridge Grammar sees modal characteristics in all six uses of these two auxiliary verbs.
A Comprehensive Grammar calls both have got and be to modal idioms. None of the other descriptions agrees.
Palmer calls be bound/''able/going/willing to and have to semi-modals. A Comprehensive Grammar calls be able/about/apt/bound/due/going/likely/meant/obliged/supposed/willing to and have to'' semi-auxiliaries. He adds, "The boundaries of this category are not clear".

Etymology

The modals can and could are from Old English can and cuþ, which were respectively the present and preterite forms of the verb cunnan. The silent l in the spelling of could results from analogy with would and should.
Similarly, may and might are from Old English mæg and meahte, respectively the present and preterite forms of magan ; shall and should are from sceal and sceolde, respectively the present and preterite forms of sculan ; and will and would are from wille and wolde, respectively the present and preterite forms of willan.
The aforementioned Old English verbs cunnan, magan, sculan, and willan followed the preterite-present paradigm, which explains the absence of the ending -s in the third-person present forms can, may, shall, and will.
The verb must comes from Old English moste, part of the verb motan. This was another preterite-present verb, of which moste was in fact the preterite. Similarly, ought was originally a past form—it derives from ahte, preterite of agan, another Old English preterite-present verb whose present tense form, ah, has also given the modern verb owe, and ought was formerly used as a preterite form of owe.
The verb dare also originates from a preterite-present verb, durran, specifically its present tense dear although in its non-modal uses in Modern English, it is conjugated regularly. However, need comes from the regular Old English verb neodian —the alternative third person form need, which has become the norm in modal uses, became common in the 16th century.

Preterite forms

The preterite forms given above do not always simply modify the meaning of the modal to give it past reference. The only one regularly used as an ordinary past tense is could when referring to ability: I could swim may serve as a past form of I can swim.
This "future-in-the-past" use of would can also occur in a main clause: I moved to Green Gables in 1930; I would live there for the next ten years.
In many cases, in order to give modals past reference, they are used together with the auxiliary have and a past participle, as in I should have asked her; You may have seen me. Sometimes these expressions are limited in meaning; for example, must have can refer only to certainty, whereas past obligation is expressed by an alternative phrase such as had to.

Indirect speech

All the preterite forms are used as past equivalents of the corresponding present-tense modal verbs in indirect speech and similar clauses requiring the rules of sequence of tenses to be applied. For example, if it were said in 1960 that People think that we will all be driving hovercars by the year 2000, it might now be reported that In 1960, people thought that we would all be driving hovercars by the year 2000.

Modal verb	Direct speech	Indirect speech
Can	He said, "Nobody can say a word."	He said that nobody could say a word.
Could	He said, "Nobody could say a word."	He said that nobody could say a word.
May	He said, "Nobody may say a word."	He said that nobody might say a word.
Might	He said, "Nobody might say a word."	He said that nobody might say a word.
Must	He said, "Nobody must say a word."	He said that nobody must/*had to say a word.*
Shall	He said, "Nobody shall say a word."	He said that nobody should/would say a word.
Should	He said, "Nobody should say a word."	He said that nobody should say a word.
Will	He said, "Nobody will say a word."	He said that nobody would say a word.
Would	He said, "Nobody would say a word."	He said that nobody would say a word.
Dare	He said, "Nobody dare say a word."	He said that nobody dared say a word.
Need	He said, "Nobody need say a word."	He said that nobody needed to say a word.
Ought	He said, "Nobody ought to say a word."	He said that nobody ought to say a word.
Used	He said, "Nobody used to say a word."	He said that nobody used to say a word.

Conditional sentences

The preterite forms of modals are used in the apodosis of counterfactual conditional sentences. The modal would is used to produce the conditional construction typically used in clauses of this type: If you loved me, you would support me. It can be replaced by could and might as appropriate.
When the clause has past reference, the construction with the modal plus have is used: If they wanted to do it, they would have done it by now.
The protasis of such a sentence typically contains the preterite form of a verb, without any modal. The modal could may be used here in its role of the preterite form of can. However, all the modal preterites can be used in such clauses with certain types of hypothetical future reference: if I should lose or should I lose ; if you would/might/could stop doing that.
Sentences with the verb wish and expressions of wish using if only... follow similar patterns to the if-clauses that are referred to above when they have counterfactual present or past reference. When they express a desired event in the near future, the modal would is used: I wish you would visit me; If only he would give me a sign.
For more information see English conditional sentences.

Second-person singular forms

often distinguished between second-person plural you and second-person singular thou. Rather as English verbs other than modal auxiliaries agree with third-person singular subjects in today's English, Early Modern English verbs in general agreed with a second-person subject that was distinctively singular. Examples from Shakespeare are shown [|below], except for motest, attested in John Dee.

	Plain present	Preterite
can	canst	couldst
dare	darest	durst
may	mayst, mayest	mightst
must	must, motest
need	needest
ought	oughtest
shall	shalt	shouldst
will	wilt	wouldst

Replacements for defective forms

As noted above, English modal verbs are defective in that they do not have any untensed form, or, for some, preterite form. However, in many cases, expressions can carry the same meaning as the modal and be used to supply the missing forms:

The modals can and could, expressing ability, can be replaced by be able to, with the appropriate inflection of be.
The modals may and might, expressing permission, can be replaced by be allowed to, again with the appropriate inflection of be.
The modal must in most meanings can be replaced by have to, with the appropriate inflection of have.
When used for futurity, will and shall can be replaced by be going to, with the appropriate inflection of be.
The modals should and ought to might be replaced by be supposed to, again with the appropriate inflection of be.

Weak forms

The modals have strong and weak forms:

can →
could →
shall →
should →
will →,
would →,
had better →,,

When shall and should are first-person replacements for will and would, they too may take the weak forms ll and d.
A combination like should have is normally reduced to or just shoulda. Also, ought to can become oughta. See weak and strong forms in English.
Most of the modals have negative inflected forms: can't, won't, etc. Although they began as weak forms, they since evolved into inflections.

Effect of negation

Either or both of two kinds of negation can apply to a construction using a modal auxiliary verb. Internal negation semantically applies to the complement of the modal. The difference between He might have overheard you and He might not have overheard you is that between "It is possible that he overheard you" and "It is possible that he did not overhear you". With internal negation, not may occur closer to the main verb. He might have not overheard you has the same meaning as He might not have overheard you. ''He could have not overheard you means "It is possible that he did not overhear you".
In contrast, external negation applies to the modal itself. The difference between He could have overheard you and He couldn't have overheard you is that between "It is possible that he overheard you" and "It is not possible that he overheard you".
Comparing You mustn't apologize and You needn't apologize, the former involves internal negation, converting the necessity from apology-making to standing your ground; the latter external negation, negating any necessity.
The two kinds of negation can be combined. He can't have not overheard you means "It is not possible that he did not overhear you".
Whether negation is internal or external depends in part on the particular verb and the strength of modality it expresses. However: "Negative interrogatives, used as questions biased towards a positive answer, have external negation irrespective of the strength of the modality A special case is in tags: We must stop soon, mustn't we?''"

Usage of specific verbs

''Can'' and ''could''

The modal verb can expresses possibility in a dynamic, deontic, or epistemic sense, that is, in terms of innate ability, permissibility, or probability. For example:

Dynamic
*Ability: You needn't struggle with your Tamil when talking to me: I can speak English
*Existential: Most siblings get along at least tolerably well, but there can be strong rivalry between them
*The reasonable/acceptable: You can be a few minutes late; nobody will mind
*The circumstantially possible: Petrol left for months in an unused car can wreck its fuel line
Deontic: Smoking is forbidden anywhere in this building, but you can smoke behind the bicycle shed
Epistemic: He did the "Ironman" in under seven hours? That can't be true.

The preterite form could is used as the past tense or remote conditional form of can in the above meanings. It is also used to express likelihood: We could be in trouble here. It is preferable to use could, may or might rather than can when expressing likelihood in a particular situation.
Both can and could can be used to make requests: Can/could you pass me the cheese? means "Please pass me the cheese". Either can be used with possibly: Can/'could you possibly' pass me the cheese? Requests with can't may sound impatient
It is common to use can with verbs of perception such as see, hear, etc., as in I can see a tree. Aspectual distinctions can be made, such as I could see it vs. I saw it.
Could have expresses counterfactual past ability or possibility: I could have told him if I had seen him; I could have told him yesterday.
Can have... is less common than may have....
Can may be negated by the addition of not, analogously to the addition of not to could, may, will and so forth. It can also be negated by inflection; its commoner inflected form is can't,, or . However, it has an alternative inflected form, cannot. Can not and cannot thus differ in placement of the single stress. Can not is more formal than can't, and does not invert with its subject.
Negated, could has the inflected form couldn't.
Negating can or could is external and negates the matrix clause, expressing inability, impermissibility or impossibility. This differs from may or might used to express possibility: It can't be true does not mean It may not be true. Thus can't is often used to express disbelief even in possibility, as must expresses belief in the certainty. When the reference is to the past, have is used: He can't/cannot have done it means "It is not possible that he did it".
With special stress, internal negation is possible: I can wear a suit, if I wish means "I am not compelled to wear a suit if I don't want to".

''May'' and ''might''

The verb may expresses possibility in either an epistemic or deontic sense, that is, in terms of probability or permissibility. For example:

The mouse may be dead means that it is possible that the mouse is now dead.
Trevor may leave if he'd prefer to play with his friends means that Trevor is permitted to leave.

May can have future as well as present reference.
The preterite form might is used as a synonym of may to express a possible circumstance. It is sometimes said that might and could express more doubt than may. For uses of might in conditional sentences, and as a past equivalent to may in such contexts as indirect speech, see above.
May can also express concession of a minor point: He may be taller than me, but he's certainly not stronger could mean "While I'd agree that he is taller than me, that is unimportant, as he's certainly not stronger."
May can indicate permission for present or future actions, or be a polite directive: You may go now. Might used in this way is milder: You might go now if you feel like it. Similarly, May I use your phone? is a request for permission; Might I use your phone? would be more hesitant or polite.
A less common use of may is optative, as in May you live long and happy.
May have indicates uncertainty about a past circumstance, whereas might have can either have that meaning or refer to possibilities that did not occur but could have.

She may have eaten the cake.
She might have eaten the cake.

May have is used for possibility, not permission.
The inflected form mayn't is obsolete. The inflected form mightn't mostly appears in the tags of tag questions and in other questions expressing doubt.
The result of negating may or might depends on whether the interpretation is epistemic or deontic. In epistemic senses, the negation is "internal", of the subordinate clause. In deontic senses, the negation is normally external, but with special stress, internal negation is possible:.

''Shall'' and ''should''

The verb shall is used in some varieties of English in place of will when the subject is first person.
With second- and third-person subjects, shall indicates a directive or prophecy: Cinderella, you shall go to the ball! It is often used in writing laws and specifications: Those convicted of violating this law shall be imprisoned for a term of not less than three years; The device shall be able to operate within a normal temperature range.
Shall is sometimes used in requests for advice or confirmation of a suggestion: Shall I read now?; What shall we wear?
Should is sometimes used as a first-person equivalent to would in the same way that shall can replace will. Should is also used for a protasis with future reference: either with the preposition if or with subject–auxiliary inversion.
Should is often used to describe an expected or recommended act or state. It can be used to give advice or to describe normative behavior, though without such strong obligatory force as must or have to. Thus, You should never lie describes a social or ethical norm. It can also express what is expected: This should work. In these uses it is equivalent to ought.
Both shall and should can be used with have in their role as first-person equivalents of will and would. Also, shall have may express an order with perfective aspect. When should is used in that way, it usually expresses something that would have been expected at some time in the past but did not in fact happen : I should have done that yesterday.
The negative inflections are shan't and shouldn't.
Negating should negates the subordinate clause: the negation is internal.
As for any modal auxiliary, a negative interrogative instead negates the matrix clause.

''Will'' and ''would''

Will often expresses futurity. Since this is an expression of time rather than modality, constructions with will are often called the future tense. For those speakers who for first-person subjects use shall to express futurity, the use of will for these indicates particular resolve.
Will can express habitual aspect or dynamic modality; for example, He will make mistakes may mean that he seems often to make them.

Will also has these uses as a modal:

It can express strong probability with present time reference, as in That will be John at the door.
It can be used to give an indirect order, as in You will do it right now.

Modal uses of the preterite form would include:

Would is used in some conditional sentences.
Expression of politeness, as in I would like to... and Would you do this?.

As a tense marker, would is used for

Future of the past, as in I knew I would graduate two years later. Would is the past form of future will as described above under.

As an aspect marker, would is used for

Expression of habitual aspect in the past, as in Back then, I would eat early and would walk to school.

Both will and would can be used with have to form the future perfect and conditional perfect forms already referred to, or to express perfective aspect in their other meanings.
The negative inflections are won't and wouldn't. For contracted forms of will and would themselves, see "Weak forms", above.
Negating will or would is "internal" and negates the subordinate clause. But as for any modal auxiliary, a negative interrogative negates the matrix clause.

''Would rather'', ''would sooner'', and ''would as soon''

Would rather, would sooner, or would as soon can take as its complement either a bare infinitival clause or a declarative content clause. They are PPIs: although I would rather not catch the virus is idiomatic, *I wouldn't rather catch the virus is distinctly strange. Whether its reference is to past, present or future, the declarative content clause complement can use the preterite: Id rather you hadn't told her that ; Id rather you didn't tell her that ; Id rather you didn't tell her that when you meet her.

''Mote'' and ''must''

Originally, mote was used to express obligation in the present, while must fulfilled this role in the past. As mote gradually disappeared from everyday usage, must took over this function in contemporary English. Today, mote, as a modal verb, remains only in a few expressions, most notably: So mote it be.
Having assumed the present sense of obligation, must differs from the central modal auxiliary verbs in lacking a preterite. It expresses obligation or necessity: You must use this form; We must try to escape. It can also express a conclusion reached by indirect evidence.
When used with have and a past participle, must has only an epistemic flavor: Sue must have left means that the speaker concludes that Sue has left. To express obligation or necessity in the past, had to or some other synonym must be used.
The negative inflection of must is mustn't. Negation of must is "internal", negating the subordinate clause:. But as for any modal auxiliary, a negative interrogative negates the matrix clause. To express the lack of requirement or obligation, the negative of have to or need can be used: You don't have to do this; You needn't do this.
Negated, must is not commonly used in an epistemic sense, where it is common to use can't instead.
Mustn't can nonetheless be used as a simple negative of must in tag questions and other questions expressing doubt: We must do it, mustn't we? Mustn't he be in the operating room by this stage?
Must and needs can occur in sequence. Hendrik Poutsma writes that "The force of must, notably that of representing the subject under pressure of an overmastering desire , is often emphasized by needs." Examples of the pair are:

The control of the Firm needs must stay within the Family.
It needs must be said that any observation made in this order shall not be taken as observations on merits
thinking it through to its ultimate logical consequences must needs lead to insoluble contradictions
''the Constitution envisions, and by extension the country as a whole must needs have, a truly high-minded Supreme Court''

''Ought''

Ought differs from the central modal auxiliary verbs both in taking as its complement a to-infinitival rather than a bare infinitival clause and in lacking a preterite.
One can't use to after ought in questions tags. It is also possible to omit to using ellipsis or in negatives.
Ought is used with meanings similar to those of should, expressing expectation or requirement.
The reduced pronunciation of ought to is sometimes spelt oughtta.
Ought can be used with have in the same way as should : You ought to have done that earlier. Ought not to or oughtn't to can be substituted for shouldn't.
Had better has a similar meaning to should and ought for a deontic meaning, but not for an epistemic meaning.
Negating ought is "internal" and negates the subordinate clause. But as for any modal auxiliary, a negative interrogative negates the matrix clause.
The use of ought as a lexical verb as in They didn't ought to go is generally thought of as restricted to nonstandard dialects but has been described as also sometimes found in informal standard usage. "Lexical ought with the dummy operator do has been condemned in British usage handbooks. . . . What this censure suggests is that lexical ought with periphrastic do is a well-established usage in colloquial ."
Data from a corpus of American and British spoken and written English of the 1980s and 1990s show that ought not to, oughtn't to and didn't ought to are rare in both American and British English, whether written or spoken. I don't think you ought to and similar are commonly used instead. In interrogatives, ought does not appear in American conversation or fiction or in British conversation. In British fiction, the modal auxiliary is used, not lexical ought with do-support.

''Need''

As a modal auxiliary verb, need is a negative polarity item, appearing in negative contexts and other contexts that do not affirm. Thus:

No one need remain silent.
We need not remain silent.
Need we remain silent?
We need remain silent.

Like must, modal need has no preterite form.
Although as a modal auxiliary verb need takes a bare infinitival clause complement, lexical verb need can take either an object complement or a to-infinitival clause complement, optionally with a subject.
Negation of need is external, negating the matrix clause. You needn't apply again does not say that there is a need not to apply, merely that there is no need to apply. So although the verb must can usually be substituted for the modal verb need, mustn't usually cannot be substituted for needn't.
Modal need can also be used with have: Need I have done that? It is most commonly used here in the negative, meaning that an action was not in fact necessary: You needn't have left that tip.
Data from a corpus of American and British spoken and written English of the 1980s and 1990s show that for negative constructions involving need, modal auxiliary need is more common in written English.
For "needs must" see under must.

''Dare''

As a modal auxiliary verb, dare is another negative negative polarity item, appearing in negative contexts and other contexts that do not affirm.
Dare is now more common as a lexical verb. Lexical verb dare takes a to-infinitival clause as its complement, and this may have a subject ; modal dare, a bare infinitival clause complement.
Negation of dare is external: what is negated is the matrix clause.
Examples of the use of modal auxiliary dare, followed by equivalents using lexical dare where appropriate:

If he dare try it, he may succeed.
If he dared try it, he might succeed.
Dare he do it?
Dared he do it?
I daren't try.
I dared not try.
How dare you!
I dare say it's true.

However, its affirmative context causes *He dared speak up to be ungrammatical.
Although seemingly less common, the negative form daredn't is still attested in use:
"I daredn't hurry," said Mr Colclough, setting us down at the station. "I was afraid of a skid."
One's so safe with such a son to con her / Through all the noises and through all the press, / Boys daredn't squirt tormenters on her dress.
Dared has supplanted an earlier preterite form, durst. Examples:
The former retired with cattle and other booty to their mountains, whither they knew well the Lowlanders durst not follow them.
Other debts I durst not face.
dizzy church-crowned central peak that time durst not touch
Durst had a negative inflected form, durstn't. Examples:

I'm under authority, you know, and durstn't overstep
the boat, where I durstn't kick for fear of poking my feet through the bottom
I durstn't go home to tell Mother Pring

Lexical verb dare is close to an NPI: She dared to speak up is much less likely than She didn't dare to speak up. And the lexical–modal distinction is blurred: "lexical dare commonly occurs in non-affirmative contexts without to": She wouldn't dare ask her father; and it also can be stranded, as in She ought to have asked for a raise, but she didn't dare.
Data from a corpus of American and British spoken and written English of the 1980s and 1990s show that dare is infrequent and "is found chiefly in fiction and conversation". In negative constructions in American fiction, lexical dare is more common. In Britain, modal auxiliary dare is. Further, negation of preterite dared is rare. In both American and British English, interrogative constructions that require subject–auxiliary inversion show inversion of auxiliary dare much more commonly than do-support of lexical dare; however, many of the instances here of auxiliary dare are of fixed formulas.

''Used''

Used is more commonly encountered as a lexical than as an auxiliary verb, particularly for younger or American speakers. The plain form use of the lexical verb is seen in Did you use to play tennis?. Although rare, its preterite perfect had used is attested. The first of The Cambridge Grammar of the English Languages five criteria for modal auxiliary verbs is irrelevant to auxiliary verb used, which fails the last three. The auxiliary verb "is also semantically quite distinct from the modal auxiliaries: the meaning it expresses is aspectual, not modal." The Cambridge Grammar does not class auxiliary used as a modal auxiliary verb.
As an auxiliary verb, used is attested in forms that lack do-support, notably in the negative form used not to or usedn't to and in the interrogative form with subject–auxiliary inversion. More recently, however, used has increasingly been treated as a lexical verb rather than an auxiliary, and therefore typically takes do-support. As a result, the negative used not to may be replaced by didn’t use to. Likewise, the interrogative form may be supplanted by do-support forms.
For more about use'', see English auxiliary verbs.

Modal idioms with ''have''

The verb had in the expression had better lacks any untensed form and hence is sometimes classed as a modal idiom, a semi-modal, or an emerging or quasi-modal verb.
Negating had better, whether by had better not or by hadn't better, normally negates the subordinate clause: it is internal. However, as for any modal auxiliary, a negative interrogative negates the matrix clause.
Had best and had rather similarly lack any untensed form. Had best is much less common than had better. Since had rather and would rather are both likely to be realized as d rather, it is rarely easy to decide which of the pair is being used.
Hendrik Poutsma adds:

I had as lief, although now antiquated and mostly replaced by I had as soon, has never fallen completely into disuse. . . . The shortening of had to d has given rise to would being sometimes substituted for it.

Frequency of use

During the second half of the 20th century, the frequencies of use of both the modal auxiliary verbs and of alternatives to them showed considerable change. A comparison of the frequencies in the British corpora LOB and FLOB, and of those in the American corpora Brown and Frown shows:
A study of modal auxiliary verbs and quasi-modals in American, British and Australian examples of a variety of genres of written and spoken English in the 1990s found that the totals were:
Commenting on a different but similar set of figures, Longman Grammar of Spoken and Written English observes of ought, need, dare, and use :

In view of the considerable attention given to these marginal auxiliaries in grammatical descriptions of English and English language teaching materials, it is worth noting how rare they are, particularly in negative and interrogative auxiliary constructions.

Deduction

In English, modal verbs as must, have, got and could/can are used to express deduction and contention. The modal verbs state how sure the speaker is about something.

You're shivering – you must be cold.
Someone must have taken the key: it is not here.
I didn't order ten books. This has to be a mistake.
These aren't mine – they've got to be yours.
It can't be a burglar. All the doors and windows are locked.

Modals at the head of chains

The verb governed by the modal may be another auxiliary. Hence, a modal may introduce a chain of verb forms in which the other auxiliaries express properties such as aspect and voice, as in He must have been given a new job. If infinitival to is regarded as an auxiliary verb, then longer chains are possible, as in He must have been encouraged to try to serve tea.

Double modals

In Standard English, since a modal auxiliary verb is followed by a verb in its plain form, it cannot be followed by a second modal auxiliary verb. Might have is grammatical, but *might must is not.
However, what appear to be sequences of modal auxiliary verbs occur. Might could, must can, might oughta, might would, must could, could oughta, might should, may can, should oughta, might can, may could, would oughta, might will, may will, may should are some of the 76 combinations attested in Southern American English. Those with might as the first modal are easily the most common, and might could is the most common of them all. Longer sequences such as might should oughta are also attested. In Britain, by contrast, the most common is would might although commonness is relative: double modal auxiliary verbs "occur only rarely in spontaneous speech, even in varieties in which they are known to be used".
The syntactic status of sequences such as might could and would might is unclear. One possibility is that might has been reanalysed by the speaker as an English adverb and thus be functioning as an adjunct.
Two rules from different grammatical models supposedly disallow the construction. Phrase structure grammar sees the surface clause as allowing only one modal verb, and main verb analysis dictates that modal verbs occur in finite forms.

Comparison with other Germanic languages

Many English modals have cognates in other Germanic languages, if often with different meanings. Unlike the English modals, however, such verbs are not generally defective:

In German: mögen, müssen, können, sollen, wollen; cognates of may, must, can, shall, and will. Although German shares five modal verbs with English, their meanings are often quite different. Mögen does not mean "be allowed" but "may" as epistemic modal and "like" as a normal verb followed by a noun phrase. It can be followed by an infinitive with the meaning of "have a desire ". Wollen means "will" only in the sense of "want " and is not used for future reference, for which werden is used instead. Müssen, können, and sollen are used similarly to English "must", "can", and "shall". The negation of müssen is a literal one in German, not an inverse one as in English": German ich muss means "I need ", and ich muss nicht accordingly means "I don't need ". In English, "have " behaves the same way, whereas English "must" expresses an interdiction when negated. brauchen is sometimes used like a modal verb, especially negated.
In Dutch: mogen, moeten, kunnen, zullen, willen; cognates of may, must, can, shall, and will.
In Danish: måtte, kunne, ville, skulle, cognates of may/must, can, will, shall. They generally have the same meanings as in English, with the exception of ville, which usually means "want ".
In Swedish: må, måsta, kunna, vilja, ska, cognates of may/might, must, can, will, shall. Their meanings generally correspond to those in English with the exception of vilja, which means "want ".

Since modal verbs in other Germanic languages are not defective, the problem of double modals does not arise: the second modal verb in such a construction simply takes the infinitive form like for any verb in the same position. Compare the following translations of English "I want to be able to dance", all of which translate literally as "I want can dance" :

Works cited

Modal
Category:Verbs by language
Modal