A modal verb (also modal, modal auxiliary verb, modal auxiliary) is a type of auxiliary verb that is used to indicate modality – that is, likelihood, ability, permission, and obligation. Examples include the English verbs can/could, may/might, must, will/would, and shall/should.
In English and other Germanic languages, modal verbs are often distinguished as a class based on certain grammatical properties.
For more detail about modals in English, see English modal verbs
A modal auxiliary verb gives more information about the function of the main verb that it governs. Modals have a wide variety of communicative functions, but these functions can generally be related to a scale ranging from possibility ("may") to necessity ("must"), in terms of one of the following types of modality:
- epistemic modality, concerned with the theoretical possibility of propositions being true or not true (including likelihood and certainty)
- deontic modality, concerned with possibility and necessity in terms of freedom to act (including permission and duty)
- dynamic modality, which may be distinguished from deontic modality, in that with dynamic modality, the conditioning factors are internal – the subject's own ability or willingness to act
The following sentences illustrate epistemic and deontic uses of the English modal verb must:
- epistemic: You must be starving. ("It is necessarily the case that you are starving.")
- deontic: You must leave now. ("You are required to leave now.")
An ambiguous case is You must speak Spanish. This may be intended epistemically ("It is surely the case that you speak Spanish", e.g. after having lived in Spain for a long time), or deontically ("It is a requirement that you speak Spanish", e.g. if you want to get a job in Spain).
Epistemic usages of modals tend to develop from deontic usages. For example, the inferred certainty sense of English must developed after the strong obligation sense; the probabilistic sense of should developed after the weak obligation sense; and the possibility senses of may and can developed later than the permission or ability sense. Two typical sequences of evolution of modal meanings are:
- internal mental ability → internal ability → root possibility (internal or external ability) → permission and epistemic possibility
- obligation → probability
Modal verbs in Germanic languages 
The following table lists the modal auxiliary verbs of standard English. Most of them appear more than once based upon the distinction between deontic and epistemic modality:
Modal auxiliary meaning contribution Example can1 deontic/dynamic modality She can really sing. can2 epistemic modality That can indeed help. could1 deontic modality He could swim when he was young. could2 epistemic modality That could happen soon. may1 deontic modality May I stay? may2 epistemic modality That may be a problem. might epistemic modality The weather might improve. must1 deontic modality Sam must go to school. must2 epistemic modality It must be hot outside. shall deontic modality You shall not pass. should1 deontic modality You should stop that. should2 epistemic modality That should be surprising. will epistemic modality She will try to lie. would epistemic modality Nothing would accomplish that.
The verbs in this list all have the following characteristics:
- They are auxiliary verbs, which means they allow subject-auxiliary inversion and can take the negation not,
- They convey functional meaning,
- They are defective insofar as they cannot be inflected, nor do they appear in non-finite form (i.e. not as infinitives, gerunds, or participles),
- They are nevertheless always finite and thus appear as the root verb in their clause, and
- They subcategorize for an infinitive, i.e. they take an infinitive as their complement
The verbs/expressions dare, ought to, had better, and need not behave like modal auxiliaries to a large extent, although they are not productive in the role to the same extent as those listed here. Furthermore, there are numerous other verbs that can be viewed as modal verbs insofar as they clearly express modality in the same way that the verbs in this list do, e.g. appear, have to, seem, etc. In the strict sense, though, these other verbs do not qualify as modal verbs in English because they do not allow subject-auxiliary inversion, nor do they allow negation with not. If, however, one defines modal verb entirely in terms of meaning contribution, then these other verbs would also be modals and so the list here would have to be greatly expanded.
Modals in English form a very distinctive class of verbs. They are auxiliary verbs like be, do, and have, but they are defective insofar as they cannot be inflected like these other auxiliary verbs, e.g. have → has vs. should → *shoulds, do → did vs. may → *mayed, etc. In clauses that contain two or more verbs, any modal that is present appears as the left-most verb in the verb catena (= chain of verbs). What this means is that the modal verb is always finite (although it is, as stated, never inflected). In the syntactic structure of the clause, the modal verb is the clause root. The following dependency grammar trees illustrate the point:
The verb catenae are in blue. The modal auxiliary in both trees is the root of the entire sentence. The verb that is immediately subordinate to the modal is always an infinitive. The fact that modal auxiliaries in English are necessarily finite means that within the minimal finite clause that contains them, they can never be subordinate to another verb, e.g.
- a. Sam may have done his homework. - The modal auxiliary may is the root of the clause.
- b. *Sam has may done his homework. - The sentence fails because the modal auxiliary may is not the root of the clause.
- a. Jim will be helped. - The modal auxiliary will is the root of the clause.
- b. *Jim is will be helped. - The sentence fails because the modal auxiliary will is not the root of the clause.
This trait of modal auxiliaries has motivated the designation defective, that is, modal auxiliaries are defective in English because they are so limited in their form and distribution. One can note further in this area that English modal auxiliaries are quite unlike modal verbs in closely related languages. In German, for instance, modals can occur as non-finite verbs, which means they can be subordinate to other verbs in verb catenae; they need not appear as the clause root.
Other West Germanic languages 
The table below lists some modal verbs with common roots in English, German, Dutch, West Frisian and Afrikaans. English modal auxiliary verb provides an exhaustive list of modal verbs in English, and German verb#Modal verbs provides a list for German, with translations. Dutch verbs#Irregular verbs gives conjugations for some Dutch modals.
Words in the same row of the table below share the same etymological root. Because of semantic drift, however, words in the same row may no longer be proper translations of each other. In addition, the English and German verbs will are completely different in meaning, and the German one has nothing to do with constructing the future tense. These words are false friends.
In English and Afrikaans, the plural and singular forms are identical. For German, Dutch, and West Frisian, both the plural and singular form of the verb are shown.
Etymological relatives (not translations)
|can||können, kann||kunnen, kan||kinne, kin||kan|
|shall||sollen, soll||zullen, zal||sille, sil||sal|
|will||wollen, will||willen, wil||wolle, wol||wil|
|must||müssen, muss||moeten, moet||moatte, moat||moet|
|may||mögen, mag||mogen, mag||meie, mei||mag|
|tharf||dürfen, darf||durven, durf||doarre, doar||durf|
The English could is the preterite form of can; should is the preterite of shall; and might is the preterite of may. (This is ignoring the use of "may" as a vestige of the subjunctive mood in English.) These verbs have acquired an independent, present tense meaning. The German verb möchten is sometimes taught as a vocabulary word and included in the list of modal verbs, but it is actually the past subjunctive form of mögen.
The English verbs dare and need have both a modal use (he dare not do it), and a non-modal use (he doesn't dare to do it). The Dutch, West Frisian, and Afrikaans verbs durven, doarre, and durf are not considered modals (but they are there, nevertheless) because their modal use has disappeared, but they have a non-modal use analogous with the English dare. Some English modals consist of more than one word, such as "had better" and "would rather".
Owing to their modal characteristics, modal verbs are among a very select group of verbs in Afrikaans that have a preterite form. Most verbs in Afrikaans only have a present and a perfect form.
Some other English verbs express modality although they are not modal verbs because they are not auxiliaries, including want, wish, hope, and like. All of these differ from the modals in English (with the disputed exception of ought (to)) in that the associated main verb takes its long infinitive form with the particle to rather than its short form without to, and in that they are fully conjugated.
Morphology and syntax 
Germanic modal verbs are preterite-present verbs, which means that their present tense has the form of a vocalic preterite. This is the source of the vowel alternation between singular and plural in German and Dutch. Because of their preterite origins, modal verbs also lack the suffix (-s in modern English, -t in German, Dutch, and West Frisian) that would normally mark the third person singular form. Afrikaans verbs do not conjugate, and thus Afrikaans non-modal verbs do not have a suffix either:
|normal verb||modal verb|
|English||he works||he can|
|German||er arbeitet||er kann|
|Dutch||hij werkt||hij kan|
|West Frisian||hy wurket||hy kin|
|Afrikaans||hy werk||hy kan|
The main verb that is modified by the modal verb is in the infinitive form and is not preceded by the word to (German: zu, Dutch, West Frisian, and Afrikaans: om te). There are verbs that may seem somewhat similar in meaning to modal verbs (e.g. like, want), but the construction with such verbs would be different:
|normal verb||modal verb|
|English||he tries to work||he can work|
|German||er versucht zu arbeiten||er kann arbeiten|
|Dutch||hij probeert te werken||hij kan werken|
|West Frisian||hy besyket te wurkjen||hy kin wurkje|
|Afrikaans||hy probeer om te werk||hy kan werk|
In English, main verbs but not modal verbs always require the auxiliary verb do to form negations and questions, and do can be used with main verbs to form emphatic affirmative statements. Neither negations nor questions in early modern English used to require do.
|normal verb||modal verb|
|affirmative||he works||he can work|
|negation||he does not work||he cannot work|
|emphatic||he does work hard||he can work hard|
|question||does he work here?||can he work at all?|
|negation + question||does he not work here?||can he not work at all?|
(German, Afrikaans, and West Frisian never use "do" as an auxiliary verb for any function; Dutch uses "do" as an auxiliary, but only in colloquial speech)
In English, modal verbs are called defective verbs because of their incomplete conjugation: they have a narrower range of functions than ordinary verbs. For example, most have no infinitive or gerund.
Modal verbs in other languages 
Hawaiian Creole English 
Hawaiian Creole English is a creole language most of whose vocabulary, but not grammar, is drawn from English. As is generally the case with creole languages, it is an isolating language and modality is typically indicated by the use of invariant pre-verbal auxiliaries. The invariance of the modal auxiliaries to person, number, and tense makes them analogous to modal auxiliaries in English. However, as in most creoles the main verbs are also invariant; the auxiliaries are distinguished by their use in combination with (followed by) a main verb.
There are various preverbal modal auxiliaries: kaen "can", laik "want to", gata "have got to", haeftu "have to", baeta "had better", sapostu "am/is/are supposed to". Unlike in Germanic languages, tense markers are used, albeit infrequently, before modals: gon kaen kam "is going to be able to come". Waz "was" can indicate past tense before the future/volitional marker gon and the modal sapostu: Ai waz gon lift weits "I was gonna lift weights"; Ai waz sapostu go "I was supposed to go".
Hawaiian, like the Polynesian languages generally, is an isolating language, so its verbal grammar exclusively relies on unconjugated verbs. Thus, as with creoles, there is no real distinction between modal auxiliaries and lexically modal main verbs that are followed by another main verb. Hawaiian has an imperative indicated by e + verb (or in the negative by mai + verb). Some examples of the treatment of modality are as follows::pp. 38–39 Pono conveys obligation/necessity as in He pono i na kamali'i a pau e maka'ala, "It's right for children all to beware", "All children should/must beware"; ability is conveyed by hiki as in Ua hiki i keia kamali'i ke heluhelu "Has enabled to this child to read", "This child can read".
French, like other Romance languages, does not have a grammatically distinct class of modal auxiliary verbs; instead, it expresses modality using conjugated verbs followed by infinitives: for example, pouvoir "to be able" (Je peux aller, "I can go"), devoir "to have an obligation" (Je dois aller, "I must go"), and vouloir "to want" (Je veux aller "I want to go").
Mandarin Chinese 
Mandarin Chinese is an isolating language without inflections. As in English, modality can be indicated either lexically, with main verbs such as yào "want" followed by another main verb, or with auxiliary verbs. In Mandarin the auxiliary verbs have six properties that distinguish them from main verbs::pp.173-174
- They must co-occur with a verb (or an understood verb).
- They cannot be accompanied by aspect markers.
- They cannot be modified by intensifiers such as "very".
- They cannot be nominalized (used in phrases meaning, for example, "one who can")
- They cannot occur before the subject.
- They cannot take a direct object.
The complete list of modal auxiliary verbs:pp.182-183 consists of
- three meaning "should",
- four meaning "be able to",
- two meaning "have permission to",
- one meaning "dare",
- one meaning "be willing to",
- four meaning "must" or "ought to", and
- one meaning "will" or "know how to".
Spanish, like French, uses fully conjugated verbs followed by infinitives. For example, poder "to be able" (Puedo andar, "I can walk"), deber "to have an obligation" (Debo andar, "I should go"), and querer "to want" (Quiero andar "I want to go").
The correct use of andar in these examples would be reflexive. "Puedo andar" means "I can walk", "Puedo irme" means "I can go" or "I can take myself off/away". The same applies to the other examples.
See also 
- The Syntactic Evolution of Modal Verbs in the History of English
- Walter W. Skeat, The Concise Dictionary of English Etymology (1993), Wordsworth Editions Ltd.
|This section requires expansion. (May 2008)|
- Palmer, F.R., Mood and Modality, Cambridge University Press, 2001, p. 33
- A Short Overview of English Syntax (Rodney Huddleston), section 6.5d
- Palmer, op. cit., p. 70. The subsequent text shows that the intended definitions were transposed.
- Bybee,Joan; Perkins, Revere; and Pagliuca, William. The Evolution of Grammar, Univ. of Chicago Press, 1994, pp.192-199
- Obsolete or dialectal, confused with and replaced by dare (OED, s.v. †tharf, thar, v. and dare, v.1).
- Ian Jacobs. English Modal Verbs. August 1995
- Sakoda, Kent, and Jeff Siegel, Pidgin Grammar, Bess Press, 2003.
- Alexander, W. D., Introduction to Hawaiian Grammar, Dover Publ., 2004
- Li, Charles N., and Sandra A. Thomson, Mandarin Chinese: A Functional Reference Grammar, 1989.
- German Modal Verbs A grammar lesson covering the German modal verbs
- (Portuguese) Modal Verbs
- Modal Verb Tutorial