Modals in Formal Language

In the English language, there is a subgroup of auxiliary or helping verbs that are used to express ability, obligation, permission, possibility, intention, request, advisability, or past habit. This subgroup of auxiliary or helping verbs is called modal verbs, modal auxiliaries, or simply, modals. Since they function as helpers, they are always followed by a main verb when used in a sentence.

Single-Word Modals		Phrasal Modals
can	could	be able to	had better
may	might	be going to	ought to
shall	should	be supposed to	used to
will	would	have to
must		have got to