This document defines modal verbs and provides examples of their usage. Modal verbs are used to indicate modality, or likelihood, ability, permission, and possibility. They can modify the meaning of the verb in the clause. The document lists common modal verbs like can, could, may, might, will, would, shall, should, ought to, and must. It discusses their structure and how they are used without additions like -s, -es, infinitives, or -ing forms. Examples are provided for how each modal verb is used, such as expressing ability, permission, possibility, necessity, suggestions, offers, promises and more.