Modal auxiliary verbs are commonly known as helping verbs that are used to convey the necessity, permission, possibility, ability, or obligation of a main verb in a sentence. Other synonyms for modal auxiliary include modal verbs, modal auxiliaries, modals, and auxiliary modals. These verbs play a crucial role in indicating the mood or attitude of a speaker towards the action being performed in a sentence. Some common modal auxiliary verbs include can, could, may, might, must, shall, should, will, and would. Understanding how to use and recognize modal auxiliary verbs is essential for effective communication in both formal and informal settings.