Modal auxiliaries are special auxiliary verbs that express the degree of certainty of the action in the sentence, or the attitude or opinion of the writer concerning the action. Some common modal auxiliaries are must, can, will, and should. The following chart lists the forms and meanings of the modal auxiliaries in English.
| Present | Past/Conditional | Meanings |
|---|---|---|
| may | might | possible, not certain, with permission (negative=not certain) |
| can | could | possible, physically able, optional (negative=not possible) |
| will | would | definite future, desired, promised |
| shall | should | probable future, intended future (conditional=morally advisable) |
| must | -- | obligatory, urgent, necessary, logical deduction |
