As a principal verb

As a principal verb do is used in the sense of perform or act.

I did my duty well.
Do as I do.
Can’t you do it yourself?

As an auxiliary verb

The auxiliary do is used in three ways.

To ask a question

The auxiliary do and its forms does and did are used to ask questions in the simple present and simple past tenses.

Read the sentences given below:

I know where John lives. (Affirmative)
Do you know where John lives? (Interrogative)
They take him for a fool. (Affirmative)
Do they take him for a fool? (Interrogative)

To form a negative statement

The auxiliary do and its forms are used to change an affirmative sentence in the simple present and simple past tense into the negative.

I saw him last week. (Affirmative)
I did not see him last week. (Negative)
They want an answer. (Affirmative)
They do not want an answer. (Negative)
He gave me a gift. (Affirmative)
He did not give me a gift. (Negative)

To emphasize an assertion

The auxiliary be is sometimes used to emphasize an assertion.

I do admit that I was wrong. (More emphatic than I admit that I was wrong.)
Do sit down.
They did say that they would help.
He did come.

Exercise

Fill in the blanks with appropriate forms of be, have and do.

1.    I will leave for Mumbai after I —————– finished my work here.

a)    Am
b)    Have
c)    Do
d)    Did

2.    She ————— playing the piano when I entered the room.

a)    Is
b)    Has
c)    Was
d)    Do

3.    The boy ——————— become unconscious before the doctor came.

a)    Had
b)    Have
c)    Did
d)    Was

4.    ——————– you ever been to Darjeeling?

a)    Do
b)    Have
c)    Were
d)    Had

5.    That is what he —————- not seem to understand.

a)    Do
b)    Does
c)    Has
d)    Had

Answers

1.    Have
2.    Was
3.    Had
4.    Have
5.    Does