Auxiliary verb

Auxiliary verb is a term in grammar for a verb that is used as a helping verb in forming a tense, mood, voice or other verb, such as is, are, was etc. There are two kinds of auxiliary verbs in English - the Primary Auxiliary, and the Modal Auxiliaries. Be (is, are, was etc), do, and have are primary auxiliaries, while can, could, may, might, must, shall, should, will, and would are modal auxiliaries.