Verbs like “do” and “have” are some of the verbs in English that can function as auxiliary verbs. If we say “Do you like shrimp?” or “I don’t like shrimp,” we are using “do” as an auxiliary verb. In these sentences, the main verb is “like.” It carries the major part of the meaning we are expressing. The function of “do” in these sentences is grammatical. It allows us to form a question or a negative (in combination with the word “not”). It also passes on to the listener the information that we are talking about the present time and not the past. An auxiliary verb, therefore, is a verb that combines with a main verb and conveys additional, mainly grammatical, information. The three regular auxiliaries that are used in English are “do,” “have,” and “be.” In the following sentences, you can see these verbs operating as auxiliaries.
I was taking a shower when they arrived. [BE]
He had been to that restaurant once before. [HAVE]
They did not report the accident to the police. [DO]
Some auxiliary verbs in English color the meaning of the main verb in certain ways. These auxiliaries are called “modal auxiliary verbs” or “modal auxiliaries” and they add to the meaning of the main verb ideas such as ability (e.g., “I can fix that”), potential (e.g., “You could be a star someday”), future time (e.g., “Winter will be here soon”), requirement (e.g., “Everyone must sign in”), and advisability (“They should do more exercise”). For more information on these types of auxiliaries see MODAL AUXILIARY.