Verbs can be either main verbs or auxiliary verbs. Main verbs tell what action is being performed in a sentence. Auxiliary verbs are used in combination with main verbs. They perform two major functions: 1. Auxiliary verbs indicate shades of meaning that cannot be expressed by a main verb alone. 2. Auxiliary verbs also show tense—the time at which the action of the verb takes place. Do you know the position that auxiliary verbs have in a sentence? They always come before the main verb, although sometimes another word, such as an adverb, may come between the auxiliary verb and the main verb.