Modal auxiliary

Modal auxiliary verbs give more information about the function of the main verb that follows it. Although having a great variety of communicative functions, 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, concerned with the theoretical possibility of propositions being true or not true (including likelihood, and certainty); and
• deontic, 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:

• epistemic: You must be starving. (e.g., "It is necessarily the case that you are starving.")
• deontic: You must leave now. (e.g., "You are required to leave now.")
• ambiguous: You must speak Spanish.
  • epistemic: "It is surely the case that you speak Spanish (after having lived in Spain for ten years)."
  • deontic: "It is a requirement that you speak Spanish (if you want to get a job in Spain)."

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."

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.^[3] 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.