Unit 12. When…? and How long…? For and since
(сравнение Past Simple и Present Perfect)

Compare When …? (+ Past Simple) and How long …? (+ Present Perfect):

A: When did it start raining?
B: It started raining an hour ago / at 1 o'clock.

A: How long has it been raining?
B: It's been raining for an hour / since 1 o'clock.

A: When did Joe and Carol first meet?
B: They first met a long time ago / when they were at school.

A: How long have Joe and Carol known each other?

B: They've known each other

for a lone time.
since they were at school.

We use both for and since to say how long something has been happening.

We use for when we say a period of time (two hours, six weeks etc.):

I've been waiting for two hours.

	for
two hours 20 minutes five days six months		a week 50 years a long time ages

Sally's been working here for six months. (not since six months)
I haven't seen Tom for three days. (not since three days)

We use since when we say the start of a period (8 o'clock, Monday, 1985 etc.):

I've been waiting since 8 o'clock.

	since
8 o'clock Monday 12 May April		1977 Christmas lunchtime they were at school

Sally's been working here since April. ( = from April until now)
I haven't seen Tom since Monday. ( = from Monday until now)

It is possible to leave out for (but not usually in negative sentences):

They've been married (for) ten years. (with or without for)
They haven't had a holiday for ten years. (you must use for)

We do not use for + all … (all day / all my life etc.):

I've lived here all my life. (not for all my life)

We say "It's (a long time / two years etc.) since something happened":

It's two years since I last saw Joe. ( = I haven't seen Joe for two years / the last time I saw Joe was two years ago)
It's ages since we went to the cinema. ( = We haven't been to the cinema for ages)

The question is How long is it since …?

How long is it since you last saw Joe? ( = When did you last see Joe?)
How long is it since Mrs ill died? ( = When did Mrs Hill die?)

See Unit 11. How long have you (been)…? (настоящее совершенное время).

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Unit 12. When…? and How long…? For and since (сравнение Past Simple и Present Perfect)

Unit 12. When…? and How long…? For and since
(сравнение Past Simple и Present Perfect)