The document discusses the use of modal auxiliary verbs in English. It explains that modal auxiliaries help to express mood or attitude and are always followed by a main verb in its root form. The document lists common modal auxiliaries like may, can, must, shall, will, should, would, could, ought to, need, used to, and dare. It provides examples of how each modal auxiliary is used to indicate permission, possibility, ability, obligation, necessity, past habits and more. The document also discusses the differences between shall and will, can and could, may and might, as well as the uses of should, would, need, used to and dare.