English modal 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 (they do not have participles or plain forms) and by their lack of the ending (''e'')''s'' for the third-person singular.

The central English modal auxiliary verbs are ''can'' (with ''could''), ''may'' (with ''might''), ''shall'' (with ''should''), ''will'' (with ''would''), and ''must''. A few other verbs are usually also classed as modals: ''ought'', and (in certain uses) ''dare'', and ''need''. ''Use'' (, rhyming with "loose") 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. (A corresponding lexical verb may have the form. For example, although the lexical verb ''need'' has a preterite form, the modal auxiliary verb ''need'' does not.)

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 (i) can invert with their subjects (notably in questions, ''Must I go?''), (ii) can be negated with ''not'' (''I must not go''; ''Must I not go?''), and (iii) have negative inflected forms (''won't'', ''wouldn't'').

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'' (as in ''Take it!'', ''I didn't take it'', and ''Don't be silly''), 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 (in present tense) 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 (as an auxiliary verb) ''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 (''It seemed to happen''), and the non-modal auxiliary verb ''have'' takes a past participial clause complement (''It has happened''), a modal auxiliary verb can, in principle, take only a bare infinitival clause (a subordinate clause with the plain form of the verb without ''to'') 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 (although ''ought'' is increasingly used with a bare infinitival clause complement).

Bare infinitival clause complements are not unique to modal auxiliary verbs. ''Do'' is a non-modal auxiliary verb that takes one (''Did you move the piano?''); ''help'' is a lexical verb that can do so (''I helped move the piano'').

Ability to occur in remote apodosis

An ''apodosis'' is the "then" half of a conditional statement. (The "if" half is the ''protasis''.) ''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 (as a doubtful or incredulous contemplation of an option for the future), 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'' 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'' (with ''could'')
* ''will'' (with ''would'')
* ''may'' (with ''might'') – although the lack in today's Standard English of a negative present inflection (*''mayn't'') means that it fails one of the criteria for auxiliary verbs
* ''shall'' (with ''should'') – although the semantic divergence of ''shall'' and ''should'' means that its success with one criterion is debatable
* ''must'' – although its lack of a preterite (see its etymology below) 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: (''Could you pass me the sauce?''; ''Without my phone I might easily be lost''; ''You should work harder''; ''I would avoid that street'').

''Ought'', ''dare'', ''need'', and ''used'' satisfy some of the criteria above, and are more (''ought'', ''dare'', ''need'') or less (''used'') 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'' (''to''); it is also used in ''have to'', which has modal meaning, but here (as when denoting possession (very broadly understood)) ''have'' only rarely follows auxiliary verb syntax;
* ''do'', see ''do''-support;
* ''to'', of ''to''-infinitival clauses (if ''to'' is a defective verb, not a subordinator).

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 (with could), may (with might), must, shall (with should) and will (with would) are, or are among, the "central modal auxiliaries" (''A Comprehensive Grammar of the English Language'', 1985), "secondary or modal auxiliaries" ( F. R. Palmer, 1988), "modal auxiliaries" (Anthony R. Warner, 1993), "central members of the modal auxiliary class" ('' The Cambridge Grammar of the English Language'', 2002), or "core modal verbs" (Bas Aarts, 2011).

Among these five verbs, ''The Cambridge Grammar'' selects the pair ''can'' and ''will'' (with ''could'' and ''would'') 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 (''would rather'', ''had better'', ''had rather'') 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 (''Ive got to go now'') and be to (''You are to hand over the cash'') modal idioms. None of the other descriptions agrees.

Palmer calls ''be bound''/''able''/''going''/''willing to'' and ''have'' (''got'') ''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''(''n'') and ''cuþ'', which were respectively the present and preterite forms of the verb '' cunnan'' ("be able"). 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'' ("may, to be able"); ''shall'' and ''should'' are from ''sceal'' and ''sceolde'', respectively the present and preterite forms of '' sculan'' ("owe, be obliged"); and ''will'' and ''would'' are from ''wille'' and ''wolde'', respectively the present and preterite forms of ''willan'' ("wish, want").

The aforementioned Old English verbs ''cunnan'', ''magan'', ''sculan'', and ''willan'' followed the preterite-present paradigm (or, in the case of ''willan'', a similar but irregular paradigm), which explains the absence of the ending ''-s'' in the third-person present forms ''can'', ''may'', ''shall'', and ''will''. (The original Old English forms given above were first- and third-person singular forms; their descendant forms have become generalized to all persons and numbers.)

The verb ''must'' comes from Old English ''moste'', part of the verb '' motan'' ("be able/obliged (to do something)"). This was another preterite-present verb, of which ''moste'' was in fact the preterite (the present form ''mot'' gave rise to '' mote'', which was used as a modal verb in Early Modern English, but ''must'' has now lost its past connotations and has replaced ''mote''). Similarly, ''ought'' was originally a past form—it derives from ''ahte'', preterite of '' agan'' ("own"), another Old English preterite-present verb whose present tense form, ''ah'', has also given the modern (regular) verb ''owe'', and ''ought'' was formerly used as a preterite form of ''owe''.

The verb ''dare'' also originates from a preterite-present verb, ''durran'' ("dare"), specifically its present tense ''dear''(''r'') although in its non-modal uses in Modern English, it is conjugated regularly. However, ''need'' comes from the regular Old English verb ''neodian'' (meaning "be necessary")—the alternative third person form ''need'' (in place of ''needs''), which has become the norm in modal uses, became common in the 16th century.

Preterite forms

The preterite forms given above (''could'', ''might'', ''should'', and ''would'', corresponding to ''can'', ''may'', ''shall'', and ''will'', respectively) 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''.

All the preterites are used as past equivalents for the corresponding present modals 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 we would all be driving hovercars by the year 2000.''

This "future-in-the-past" (also known as the past prospective) 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'' (see below).

Conditional sentences

The preterite forms of modals are used in the apodosis (''then''-clause) of counterfactual conditional sentences. The modal ''would'' (or ''should'' as a first-person alternative) 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'' (meaning "would be able (to do something)") and ''might'' (meaning "would possibly") as appropriate.

When the clause has past reference, the construction with the modal plus ''have'' (see above) is used: ''If they (had) wanted to do it, they would (could/might) have done it by now.'' (The ''would have done'' construction is called the conditional perfect.)

The protasis (''if''-clause) of such a sentence typically contains the preterite form of a verb (or the past perfect construction, for past reference), without any modal. The modal ''could'' may be used here in its role of the preterite form of ''can'' (''if I could speak French''). 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'' (equivalent to ''if I lose''); ''if you would/might/could stop doing that'' (usually used as a form of request).

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

Early Modern English often distinguished between second-person plural ''you'' (or '' ye'') 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 (modal auxiliaries included) agreed with a second-person subject that was distinctively singular. (There was no such agreement with instances of ''you'' or ''ye'' that happened to have singular reference.) Examples from Shakespeare are shown below.

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'' 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

Most of the modals have negative inflected forms: ''can't'', ''won't'', etc. Although they started as weak forms ( contractions), they are no longer so. Genuine contractions are:

* ''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.

Effect of negation

Either or both of two kinds of negation can apply to a construction using a modal auxiliary verb. What is called internal negation is limited to the subordinate clause. The difference between ''He might have overheard you'' and ''He might not have overheard you'' (with internal negation) is that between "It is possible that he overheard you" and "It is possible that he did not overhear you".

By contrast, what is called external negation applies to the matrix clause. The difference between ''He could have overheard you'' and ''He couldn't have overheard you'' (with external negation) is that between "It is possible that he overheard you" and "It is not possible that he overheard you".

''Not'' can be moved into the subordinate clause. ''He might have not overheard you'' has the same meaning as ''He might not have overheard you''; but ''He could have not overheard you'' means "It is possible that he did not overhear you".

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".

Likewise, the difference between ''You mustn't apologize'' and ''You needn't apologize'' is that the former shows internal negation, inverting the necessity; the latter external negation, negating the necessity.

Whether negating a modal auxiliary verb brings negation of the subordinate or the matrix clause (internal or external negation respectively) thus depends on the particular verb, which in turn partly depends on the strength of the modality that the verb expresses, and there may be other determining factors as well. 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'' ("I am capable of speaking English"; "I know how to speak English")
**Existential: ''Most siblings get along at least tolerably well, but there can be strong rivalry between them'' (such rivalry does sometimes occur)
**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'' (This is the result of a predictable chemical process that is not being prevented.)
*Deontic: ''Smoking is forbidden anywhere in this building, but you can smoke behind the bicycle shed'' ("You are permitted to smoke here")
*Epistemic: ''He did the "Ironman" in under seven hours? That can't be true.'' ("It is impossible for that to be true.")

The preterite form ''could'' is used as the past tense or remote conditional form of ''can'' in the above meanings (see above). 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 (as opposed to the general case, as in the "rivalry" example above, where ''can'' or ''may'' is used).

Both ''can'' and ''could'' can be used to make requests: ''Can/could you pass me the cheese?'' means "Please pass me the cheese" (where ''could'' is more polite). Either can be used with ''possibly'': ''Can/could you possibly pass me the cheese?'' Requests with ''can't'' may sound impatient (''Can't you be quiet?'')

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'' (ongoing state) vs. ''I saw it'' (event).

''Could have'' expresses counterfactual past ability or possibility: ''I could have told him if I had seen him''; ''I could have told him yesterday'' (but I didn't).

''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 (in RP, General American and General Australian respectively). 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 (''Can't/*Cannot we leave now?'').

Negated, ''could'' has the inflected form ''couldn't''.

Negating ''can'' or ''could'' is external and negates the matrix clause, expressing inability, impermissibility or impossibility (''I can't wear jeans''). 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'' (or ''cannot'') 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" (compare ''He must have done 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 (perhaps audible until the day before) 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 (''He may arrive'' means that it is possible that he will arrive; ''I may go to the mall'' means that I am considering going to the mall).

The preterite form ''might'' is used as a synonym of ''may'' to express a possible circumstance (as can ''could'' – see above). 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'' (or ''might'') 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 (to express a wish), as in ''May you live long and happy'' (see also English subjunctive).

''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 (see also conditional sentences above).
* ''She may have eaten the cake.'' (The speaker does not know whether she did.)
* ''She might have eaten the cake.'' (The speaker either does not know whether she did, or knows that she did not eat cake but that her eating it would have been possible.)

''May have'' is used for possibility, not permission (although the second sense of ''might have'' might sometimes imply permission).

The inflected form ''mayn't'' is obsolete. The inflected form ''mightn't'' mostly appears in the tags of tag questions (''It might snow tonight, mightn't it?'') and in other questions expressing doubt (''Mightn't I come in if I took my boots off?'').

The result of negating ''may'' or ''might'' depends on whether the interpretation is epistemic (about likelihood) or deontic (about permission). In epistemic senses, the negation is "internal", of the subordinate clause (''There may not be a vote on it this week''). In deontic senses, the negation is normally external (''You may not go to the party unless you finish your homework''), but with special stress, internal negation is possible: (''I may attend church, if I wish'', meaning "I have permission not to attend church").

''Shall'' and ''should''

The verb ''shall'' is used in some varieties of English in place of ''will'' when the subject is first person (''I shall, we shall'').

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 its conditional and "future-in-the-past" uses) in the same way that ''shall'' can replace ''will''. ''Should'' is also used for a protasis with future reference: either with the preposition ''if'' (''If you should meet her, please give her this'') or with subject–auxiliary inversion (''Should you meet her, please give her this'').

''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'' (''shall/should have'' (''done'')) in their role as first-person equivalents of ''will'' and ''would'' (thus to form future perfect or conditional perfect structures). Also, ''shall have'' may express an order with perfective aspect (''You shall have finished your duties by nine o'clock''). 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 (or is not known to have happened): ''I should have done that yesterday'' ("It would have been expedient, or expected of me, to do that yesterday").

The negative inflections are ''shan't'' and ''shouldn't''.

Negating ''should'' negates the subordinate clause: the negation is internal (''You shouldn't use botox''). (To negate the meaning of ''I should'', one may use''I ought not to'' or ''I am not supposed to''.)

As for any modal auxiliary, a negative interrogative (''Shouldn't you check your credit card statement?'') instead negates the matrix clause.

''Will'' and ''would''

* ''Will'' often expresses futurity (''The next meeting will be held on Thursday''). Since this is an expression of time rather than modality, constructions with ''will'' (or sometimes ''shall''; see " ''Shall'' and ''should''" above) are often called the future tense. For those speakers who for first-person subjects (''I'', ''we'') use ''shall'' to express futurity, the use of ''will'' for these indicates particular resolve. (Future events are also sometimes described with the present tense (see Uses of English verb forms), or using the ''going to'' construction.)
* ''Will'' can express habitual aspect or dynamic modality; for example, ''He will make mistakes'' (in which ''will'' is usually stressed somewhat) 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...'' (to politely state a preference) and ''Would you (be so kind as to) do this?'' (for "Please 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 . (It is sometimes replaced by ''should'' in the first person in the same way that ''will'' is replaced by ''shall''.)

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'' (''will have'', ''would have'') to form the future perfect and conditional perfect forms already referred to, or to express perfective aspect in their other meanings (e.g. ''there will have been an arrest order'', expressing strong probability).

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. (''I won't be surprised if it rains'' means ''I will be unsurprised if it rains''.) But as for any modal auxiliary, a negative interrogative (''Won't''/''Wouldn't we submit them in person?'') 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 (''She would rather go herself'') or a declarative content clause (''She would rather ''(''that'')'' I went''). They are PPIs: although ''I would rather not catch the virus'' (with negation of the clause that is subordinate to ''would rather'') is idiomatic, *''I wouldn't rather catch the virus'' (with negation of the matrix clause) 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'' (past counterfactual); ''Id rather you didn't tell her that'' (present/future); ''Id rather you didn't tell her that when you meet her'' (future).

''Must''

''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 (e.g. ''Sue must be at home'').

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: (''You must not/mustn't drive after smoking a joint'' means that not driving is what you must do). But as for any modal auxiliary, a negative interrogative (''Mustn't we hide the dope?'') negates the matrix clause. To express the lack of requirement or obligation, the negative of ''have to'' or ''need'' (see below) 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'' (''It can't be here''; ''Sue can't have left'') 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 (compare ''He should go'' with ''He ought to go'') and in lacking a preterite.

''Ought'' is used with meanings similar to those of ''should'', expressing expectation or requirement.

The reduced pronunciation of ''ought to'' (see " Weak forms" above) is sometimes spelt ''oughtta''.

''Ought'' can be used with ''have'' in the same way as ''should'' (plus intervening ''to''): ''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 (expressing recommended or expedient behavior (''You ought to ''/'' should ''/'' had better arrive on time''), but not (other perhaps than jokingly) for an epistemic meaning (''The Sun ought to ''/'' should ''/ ?''had better come out soon'').

Negating ''ought'' is "internal" and negates the subordinate clause (''I ought not to have a third glassful'' means that what I ought to do is decline the glassful). But as for any modal auxiliary, a negative interrogative (''Oughtn't we to offer cola as well as beer?'') 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 ritish English"

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'' (both modal auxiliary) 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 (''Ought we to . . . ?''), 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:
* ''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 (''He needn't overhaul it''), lexical verb ''need'' can take either an object complement (''He needs my help'') or a ''to''-infinitival clause complement (''He needs to overhaul it''), optionally with a subject (''He needs me to overhaul it'').

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''. (Exceptionally, the pair are synonymous in polar interrogatives: ''Needn't/mustn't we pay now?'')

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 (from the present perspective) 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 (both American and British, but is less common than lexical ''need'' in British English conversation and unused in American English conversation.163 In both American and British English, interrogative constructions that require subject–auxiliary inversion show ''do''-support of lexical ''need'' much more commonly than inversion of auxiliary ''need''; moreover, many of what instances there are of auxiliary ''need'' are of fixed formulas (''Need I say more?'', etc).

''For "needs must" (and "must needs") 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 much more common as a lexical verb. Lexical verb ''dare'' takes a ''to''-infinitival clause as its complement (''I didn't dare to answer her''), and this may have a subject (''He dared me to dive from a higher board''); modal ''dare'', a bare infinitival clause complement.

Negation of ''dare'' is external: what is negated is the matrix clause. (''She dare not attempt it'' means "She doesn't dare to attempt it".)

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 dares to try it, he may succeed.")
*''If he dared try it, he might succeed.'' ("If he dared to try it, he might succeed.")
*''Dare he do it?'' ("Does he dare to do it?")
*''Dared he do it?'' ("Did he dare to do it?")
*''I daren't'' (or ''dare not'') ''try.'' ("I don't dare to try.")
*''I dared not try.'' ("I didn't dare to try.")
*''How dare you!'' (formulaic expression of outrage)
*''I dare say'' (or ''daresay'') ''it's true''. (Another formulaic expression, here exceptionally in an affirmative context, unexpected for an NPI)

However, its affirmative context causes *''He dared speak up'' to be ungrammatical.

Although seemingly obsolete in the 21st century, ''daredn't'' was in use in the early 20th:

*''"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'' (modal or lexical) is infrequent and "is found chiefly in fiction and ritish Englishconversation". 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 (''How dare you . . . ?'', etc).

''Used''

Used is far more commonly encountered as a lexical than as an auxiliary verb, particularly for younger or American speakers. The plain form ''use'' (sometimes spelt ) 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 Language''s 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.

For more about ''use'', see English auxiliary verbs.

Modal idioms with ''have''

The verb ''had'' in the expression ''had better'' lacks any untensed form (*''Tomorrow you will have better concentrate''; *''I've had better work hard since I started''; *''We're having better concentrate'') 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 (''Youd better not stick around''). However, as for any modal auxiliary, a negative interrogative (''Hadn't we better scarper before the police come?'') 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'' (or ''lieve''), 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 (with material from 1961 and 1991 respectively), and of those in the American corpora Brown and Frown (1961 and 1992 material respectively) shows:

(Percentage changes shown in parentheses come with values of greater than 0.05; they are of less statistical significance.)

A study of modal auxiliary verbs and quasi-modals in American, British and Australian examples (given equal weight) 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 (necessarily one that can appear in plain form—this includes ''be'' and ''have'', but not another modal, except in the non-standard cases described below under ). 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 (which modals lack), it cannot be followed by a second modal auxiliary verb. ''Might have'' is grammatical (''have'' is here the plain form of a non-modal verb), 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 adverbs 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: ; cognates of ''may'', ''must'', ''can'', ''shall'', and ''will''. Although German shares five modal verbs with English, their meanings are often quite different. 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 (to do something)". means "will" only in the sense of "want (to do something)" and is not used for future reference, for which is used instead. , and are used similarly to English "must", "can", and "shall". The negation of is a literal one in German, not an inverse one as in English": German ("I must") means "I need (to do something)", and (literally "I must not") accordingly means "I don't need (to do something)". In English, "have (to do something)" behaves the same way, whereas English "must" expresses an interdiction when negated. (need) is sometimes used like a modal verb, especially negated ( "He need not come.").
* In Dutch: ; cognates of ''may'', ''must'', ''can'', ''shall'', and ''will''.
* In Danish: , cognates of ''may/must'', ''can'', ''will'', ''shall''. They generally have the same meanings as in English, with the exception of , which usually means "want (to do something)" (but can also mean "will").
* In Swedish: (past tense: ), , cognates of ''may/might'', ''must'', ''can'', ''will'', ''shall''. Their meanings generally correspond to those in English with the exception of , which means "want (to do something)".

Since modal verbs in other Germanic languages are not defective, the problem of ''double modals'' (see above) 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" (except the German, as "I want dance can"):
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*
*
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{{DEFAULTSORT:English modal auxiliary verbs
Modal
Verbs by language
Modal