Glossary: modal verb
A modal verb is an auxiliary verb which expresses modality (meanings to do with what is possible, necessary, and so on).
Modal verbs are used to change the meaning of other verbs. They can express meanings such as certainty, ability, or obligation. The main modal verbs are will, would, can, could, may, might, shall, should, must and ought. A modal verb only has finite forms and has no suffixes (e.g. I sing – he sings, but not I must – he *musts).
- I can do this maths work by myself.
- This ride may be too scary for you!
- You should help your little brother.
- Is it going to rain? Yes, it might.
- *Canning swim is important. [not possible because can must be finite; contrast: Being able to swim is important, where being is not a modal verb]