Modal verbs are used to show the speaker’s attitude toward the action or state indicated by the infinitive, i. e. they show that the action indicated by the infinitive is considered as possible, impossible, probable, improbable, obligatory, necessary, advisable, doubtful or uncertain, etc.
The modal verbs are:
- can (could),
- may (might),
- must,
- should & ought,
- shall,
- will,
- would,
- need,
- dare,
- to be + Infinitive,
- have+ Infinitive.
Modal verbs are called defective because all of them (except dare and need) lack verbals and analytical forms (i. e. compound tenses, analytical forms of the Subjunctive Mood, the Passive Voice). Besides they do not take – s in the third person singular. They also have the following peculiarities:
- All of them (except ought and sometimes dare and need) are followed by the infinitive without the particle to.
- All of them (except dare and need) form the negative and the interrogative form without the auxiliary do.
- All the modal verbs have two negative forms — a full one and a contracted one:
| Full | Short | Full | Short |
|---|---|---|---|
| should not | shouldn’t | may not | mayn’t |
| must not | mustn’t | need not | needn’t |
| dare not | daren’t | cannot | can’t |
| shall not | shan’t | will not | won’t |