This document discusses modal verbs and how they are used. It defines modal verbs as auxiliary verbs that indicate modality or likelihood, ability, permission, or possibility. The document lists common modal verbs like can, could, may, might, will, would, shall, should, ought to, and must. It explains the structure of modal verbs in sentences and how they are used without suffixes or auxiliaries. Specific uses of each modal verb are described through examples, such as using can for ability or permission, could for permission or possibility, and may for permission.