Do, Does and Did

Few small words work as hard in English as "do". It is the auxiliary that builds most questions and negatives in the present and past simple, it adds emphasis, and it is also a full main verb in its own right. Getting "do" and "does" right is one of the earliest wins in learning English, because you need them in almost every question you ask. This guide explains the forms of "do", when to use "do" and when "does", and how the verb works in questions, negatives, short answers, emphasis and as a main verb, with examples throughout.

The forms of “do”

"Do" has three forms you need. In the present simple it is "do" for I, you, we and they, and "does" for he, she and it. In the past simple it is "did" for every person. The negative contractions are "don't", "doesn't" and "didn't".

Do or does: which to use

The choice in the present simple depends only on the subject. Use "does" with the third person singular, he, she and it, and "do" with everyone else. So it is "I do", "they do" and "we do", but "she does" and "it does". In the past simple there is no choice at all, because "did" is used for every subject.

Do and does in questions

To form a question in the present simple, put "do" or "does" before the subject, followed by the main verb in its base form: "Do you live here?", "Does she work on Fridays?". In the past, use "did": "Did they arrive on time?". The main verb never changes, so it is "Does he play", not "Does he plays".

Do and does in negatives

To make a negative, add "not" to "do" or "does", usually contracted: "I don't agree", "she doesn't drive", "we didn't know". Again the main verb stays in its base form, so it is "he doesn't want", not "he doesn't wants".
Short answers
English answers yes and no questions with "do", "does" or "did" rather than repeating the main verb: "Do you like it?" "Yes, I do." "Does she know?" "No, she doesn't." "Did they win?" "Yes, they did." The short answer simply echoes the auxiliary from the question.

Emphatic "do"
"Do", "does" and "did" can also add emphasis to a positive statement, stressing that something is true: "I do like it", "she does care", "we did try". Here the auxiliary is spoken with stress and contradicts a doubt, rather than forming a question or a negative.

"Do" as a main verb
"Do" is also a full verb meaning to perform an action or task: "I do the shopping on Saturdays", "she did her homework". This can produce two forms of "do" in one question, one auxiliary and one main, as in "What do you do?" and "What did you do yesterday?".

Common mistakes

The commonest error is marking the verb twice. Because "does" and "did" already carry the tense, the main verb stays in its base form: write "Does she like it?", not "Does she likes it?", and "Did he go?", not "Did he went?". Watch for this in both questions and negatives.