Present perfect tense for continuing situation

We often use the present perfect tense to talk about a continuing situation. This is a state that started in the past and continues in the present (and will probably continue into the future). This is a state (not an action). We usually usefor or since with this structure.

I have worked here since June. He has been ill for 2 days. How long have you known Tara?
past	present	future
~
The situation started in the past.	It continues up to now.	(It will probably continue into the future.)

Connection with past:. the situation started in the past

Connection with present:.the situation continues in the present.

For & Since with Present Perfect Tense

We often use for and since with the present perfect tense.

• We use for to talk about a period of time—5 minutes, 2 weeks, 6 years.

• We use since to talk about a point in past time—9 o'clock, 1st January, Monday.

for	since
a period of time	a point in past time
~	x----------
20 minutes	6.15pm
three days	Monday
20 minutes	6.15pm
three days	Monday
20 minutes	6.15pm
three days	Monday
6 months	January
4 years	1994
2 centuries	1800
a long time	I left school
ever	the beginning of time
etc	etc

Here are some examples:

I have been here for 20 minutes.

I have been here since 9 o'clock.

John hasn't called for 6 months.

John hasn't called since February.

He has worked in New York for a long time.

He has worked in New York since he left school.