Function of modal verbs

Modal verbs give additional information about the mood of the main verb that follows it. In other words, they help to incorporate or add the level of necessity: (must/need to/(have) got to/have to = obligation, requirement, no choice); (should/ought to = recommendation); (can/could = it is possible); and (may/might = option, choice).

Most modal verbs have two distinct interpretations, epistemic (expressing how certain is the factual status of the embedded proposition) and deontic (involving notions of permission and obligation). The following sentences illustrate the two uses of 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.")
* ambiguous: You must speak German.
o epistemic = "It is surely the case that you speak German (e.g., after having lived in Austria for 10 years)."
o deontic = "It is a requirement that you speak German (e.g., if you want to get a job in Austria)."

Epistemic modals can be analyzed as raising verbs, while deontic modals can be analyzed as control verbs.
This short section requires expansion.