What is a helping verb?

A helping verb (aka auxiliary verb) is a verb such as “do,” “have,” or “be” that’s used in combination with another verb to modify its meaning. This other verb is called the main verb. For example, in the sentence “Do you think so?” the helping verb “do” modifies the main verb “think.”

Modal verbs are a special kind of helping verbs. Unlike other helping verbs, each modal verb has only one form and can’t be conjugated. The main modal verbs are can, could, may, might, must, ought to, shall, should, will, and would (e.g., “We must leave now”).