Present continuous tense

Sentences in the present continuous tense have the following structure:

Subject + is/am/are + -ing form of the verb

She is swimming.
The water is boiling.
We are waiting.
It was surprising.
He was sulking.
You are wasting your time.

Note that we use is with singular subjects, am with I and are with you and plural subjects.

A negative sentence in the present continuous tense has the following structure:

Subject + is/am/are + not + -ing form of the verb

She is not swimming.
The water is not boiling.
We are not waiting.
It was not surprising.
He was not sulking.

Notes

In informal speech and writing, the contracted forms isn’t and aren’t are more common than the uncontracted forms is not and are not.

Present perfect tense

The present perfect tense is used to talk about past actions that cannot be attributed to a definite time. Sentences in the present perfect tense have the following structure:

Subject + has/have + past participle form of the verb

I have read all the plays of Bernard Shaw.
He has finished his work.
I have seen him before.
He has written several books.

Negative sentences in the present perfect tense have the following structure:

Subject + has/have + not + past participle form of the verb

I have not read all the plays of Bernard Shaw.
He has not finished his work.
I have not seen him before.
He has not written several books.

Notes

Have is used with I, we, you and plural subjects. Has is used with singular subjects.

The contracted forms haven’t (instead of have not) and hasn’t (instead of has not) are common in informal speech and writing.

I haven’t seen him before.
He hasn’t finished his work.

Present perfect continuous tense

The present perfect continuous tense is used to talk about an action which started in the past, has gone on till the present and is still continuing.
Sentences in this tense have the following structure:

Subject + has/have + been + ing form of the verb

He has been working since morning.
It has been raining since yesterday.
She has been reading for several hours.
We have been waiting for ages.

Negative sentences in the present perfect continuous tense have the following structure:

Subject + has/have + not + been + -ing form of the verb

He has not been working since morning.
It has not been raining since yesterday.
She has not been reading for several hours.
We have not been waiting for ages.