1. We use the present simple:

• to talk about something happening regularly in the present:

The children come home from school at about four.
We often see your brother at work.

• to talk about something happening continually in the present:

They live next door to us.
He works for the Post Office.

• to talk about things which are generally true:

Water boils at 100 degrees Celsius.
The Nile is the longest river in Africa.

2. We use the present continuous:

• to show that something in the present is temporary:

We are living in a rented flat at present.
My wife usually goes in to the office, but she is working at home today.

• for something happening regularly in the present before and after a given time:

I’m usually getting ready for work at eight o’clock.
When I see George he’s always reading his newspaper.

• for something happening before and after the moment of speaking:

I can’t hear you. I’m listening to my iPod.
Be quiet. The children are sleeping.

3. We use modal verbs

• to talk about the present when we are not sure of something:

I don’t know where Henry is. He might be playing tennis.
Who’s knocking at the door? I don’t know. It could be the police.

Exercise