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/or obligation.^[1]:p.33 The use of auxiliary verbs to express modality is particularly characteristic of Germanic languages. In English, the modal auxiliary verbs from a distinctive class because they are defective; they cannot be inflected, nor do they have non-finite forms. In other words, a modal auxiliary in English is always a non-inflected finite verb.

  List of modal auxiliaries in English

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 suprising.
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:

1. They are auxiliary verbs, which means they allow subject-auxiliary inversion and can take the negation not,
2. They convey functional meaning,
3. 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),
4. They are nevertheless always finite and thus appear as the root verb in their clause, and
5. 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.

  Meaning contribution

A modal auxiliary verb gives more information about the function of the main verb that follows it. Although they have a great variety of communicative uses, these functions can all be related to a scale ranging from possibility (may) to necessity (must). Within this scale there are two functional divisions:

• Epistemic modality: concerned with the theoretical possibility of propositions being true or not true (including likelihood, and certainty); and
• Deontic modality: concerned with possibility and necessity in terms of freedom to act (including ability, permission, and duty)

The following sentences illustrate the two uses of must:

• Deontic: You must leave now. = 'You are required to leave now.'
• Epistemic: You must be starving. = 'It is necessarily the case that you are starving.'

Ambiguous

• Deontic: You must speak Spanish. = 'It is a requirement that you speak Spanish (if you want to get a job in Spain).'
• Epistemic: You must speak Spanish. = 'It is surely the case that you speak Spanish (after having lived in Spain for ten years).'

Epistemic modals can be analyzed as raising verbs, while deontic modals can be analyzed as control verbs.

Another use of modal auxiliaries is to indicate dynamic modality, which refers to properties such as ability or disposition.^[2] Some examples of this are can in English, können in German, and possum in Latin. For example, I can say that in English, Ich kann das auf Deutsch sagen, and Illud Latine dicere possum.

  Defective

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 homeowork. - 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 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.

  Etymological relatives of Germanic

The table below lists some modal verbs with common roots in English, German and Dutch. The article English modal auxiliary verb provides an exhaustive list of modal verbs in English and the article German verb#Modal verbs provides a list for German, with translations. The article 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; the German will one has nothing to do with constructing the future tense. These words are false friends. In English, the plural and singular forms are identical. For German and Dutch, both the plural and singular form of the verb are shown.

English	German	Dutch
can	können, kann	kunnen, kan
shall	sollen, soll	zullen, zal
will	wollen, will	willen, wil
must	müssen, muss	moeten, moet
may	mögen, mag	mogen, mag
tharf[3]	dürfen, darf	durven, 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 Dutch verb durven is not considered a modal (but it is there, nevertheless) because its modal use has disappeared, but it has a non-modal use analogous with the English dare.

Despite the etymological relatedness of these verbs across the Germanic languages, the modal verbs in German and Dutch (and other Germanic languages) are much different than their English counterparts. The German and Dutch modals are not near as defective; they can be inflected to an extent and they appear as infinitives and participles, as illustrated now with the dependency grammar trees of two German sentences:

The first tree on the left is noteworthy because it contains the two modal verbs muss and dürfen, whereby muss is finite and dürfen is a non-finite infinitive. The second tree is noteworthy because the modal verb gekonnt is in participle form. The English translations of these sentences must use other, non-modal verbs (i.e. have to be allowed to and able to) because the English modals never occur as infinitives or participles.

  Evolution of modals

Deontic (agent-oriented) usages of modals tend to develop earlier than epistemic uses, and the former give rise to the latter.^{[4]:pp.192-199} 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 sense 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

  Modals in non-Germanic languages

  French

French, like other Romance languages (and like German and Dutch), has no modal auxiliary verbs in the sense that English has them. Instead, it expresses modality using conjugated verbs followed by infinitives: for example, pouvoir 'to be able', devoir 'to have an obligation', and vouloir 'to want':

a.	Je	peux	aller.
	I	can	go
b.	Je	dois	aller.
	I	should	go
c.	Je	veux	aller.
	I	want to	go

The finite verbs peux, dois, and veux convey agreement with the subject je (1st person singular). In other words, these verbs can be inflected. The English modals, in contrast, are invariable in this area, as emphasized above.

  Spanish

Spanish, like French, uses fully conjugated verbs followed by infinitives, e.g.

a.	Puedo	andar.
	(I) can	go
b.	Deber	andar.
	(I) should	go
c.	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.

  References

  References

• 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)

  See also

• English modal auxiliary verb
• Grammatical mood
• Linguistic modality
• Modal logic
• Semi-modal
• List of English auxiliary verbs

  External links

• German Modal Verbs A grammar lesson covering the German modal verbs
• (Portuguese) Modal Verbs
• Modal Verb Tutorial