Modal verbs are used to express ideas like ability, permission, possibility, obligation, and recommendation. The main modal verbs are can, could, may, might, must, shall, should, will, would, and ought to. They are sometimes called auxiliary verbs because they provide additional meaning to the main verb. Modal verbs do not conjugate or use other auxiliary verbs like do/does. They are followed by the base form of the main verb. Their meaning can be single or double depending on context. Modals are also used in the past to talk about past ability or necessity.