English sentences can have main verbs, auxiliary verbs (also called helping verbs) and compound verbs. Let's go over each group. Auxiliary Verbs. (also called helping verbs) Auxiliary verbs are verbs that are used together with another verb (called the main verb of the sentence) to express the action or state. Main verb + auxiliary verb = complete idea. The most common auxiliary verbs are: be, am, is, are, was, were, do, did, have, has, had.