Uses of the verb do

Read the following sentences in the simple present tense.

• I walk. I don’t drive. Do I walk? Yes, I do. Do I drive? No, I don’t drive.
• He speaks English. He does not speak French. Does he speak English? Yes, he does. Does he speak French? No, he doesn’t.
• I like coffee. I do not like tea. Do I like coffee? Yes, I do. Do I like tea? No, I don’t.
• Birds fly. Animals don’t fly. Do birds fly? Yes, they do. Do animals fly? No, they don’t.
• Cats chase mice. Cats don’t chase dogs. Do cats chase mice? Yes, they do. Do cats chase dogs? No, they don’t.

The auxiliary verb do is used to make questions and negative sentences in the simple present tense. Does is the singular form of do.
Note that don’t and doesn’t are the contracted forms of do not and does not.
In the sentences given above, do is used as an auxiliary verb. Do can also be used as the main verb in affirmative clauses. When do is used as a main verb, it can refer to any kind of activity.

• Do your homework.
• He does his work diligently.
• He did his job well.
• I do my homework in the evening.
• Who did this?
• I have cooked the meals, and I will do the dishes now.

Do as a substitute verb
In British English, do can also be used as a substitute for the main verb after an auxiliary.

• ‘Do you think she will recognize me?’ ‘She might do.’ (= She might recognize you.)

In American English, do is not normally used like this.

• ‘Do you think our team will win?’ ‘They might do.’ (GB) ‘They might.’ (US)

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