Modal verbs are auxiliary verbs that provide additional meaning to the main verb of a sentence. There are several modal verbs including can, could, may, might, must, shall, should, will, would, and ought to. Modal verbs do not conjugate or take other auxiliary verbs. They are used to express concepts like permission, obligation, possibility, ability, advice, and past habits. Modal verbs are categorized as single concept, double concept, or past modals depending on their meaning. Examples are provided to illustrate the different uses and meanings of various modal verbs.