org/wiki/Auxiliary_verb Do, does, or did plays a dummy (place-filling) role in transforming affirmative sentences with simple (one-word) verbs into questions or negatives . If an affirmative statement has a two-word verb (auxiliary plus main verb), a question is formed by inverting the order of the subject and the auxiliary, and a negative is formed by inserting "not" between the auxiliary and the main verb. But in the absence of an auxiliary verb, the dummy "do" is inserted as an auxiliary for either of these purposes: for example, "I go" ?
New words, one handy idiom, and a 2-minute quiz — delivered to your inbox to keep your streak alive.