Editing Modal verb (section)

==Function==
Modal verbs 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]],<ref name="lel.ed.ac.uk">[http://www.lel.ed.ac.uk/grammar/overview.html A Short Overview of English Syntax (Rodney Huddleston)], section 6.5d</ref> 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<ref>Palmer, ''op. cit.'', p. 70. The subsequent text shows that the intended definitions were transposed.</ref>

The following  sentences illustrate epistemic and deontic uses of the English modal verb ''must'':
*epistemic: ''You '''must''' be starving.'' ("I think it is almost a certainty that you are starving.")
*deontic: ''You '''must''' leave now.'' ("You are required to leave now.")
An ambiguous case is ''You must speak Spanish.'' The primary meaning would be the deontic meaning ("You are required to speak Spanish.") but this may be intended epistemically ("It is surely the case that you speak Spanish").
Epistemic modals can be analyzed as [[raising verb]]s, while deontic modals can be analyzed as [[control verb]]s.

Epistemic usages of modals tend to develop from deontic usages.<ref>Bybee, Joan; Perkins, Revere; and Pagliuca, William. ''The Evolution of Grammar'', Univ. of Chicago Press, 1994, pp.192-199</ref> 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