Verbs such as can, will, should, must, need to and be allowed to are examples of modal verbs.
Modal verbs are used with another verb. The second verb will be in the infinitive form (first form).
- I can speak English
- I am allowed to leave early
- I should be finished soon.
Modals can be used to express intention (will, should), obligation (must, have to, should, ought to), ability, (can, was able to), or permission (am allowed to, can, may).
Modals are 'imperfect' verbs, they do not decline like other verbs. The past form of ‘must’ is ‘had to’; the future form of ‘can’ is ‘will be able to’.