1 for
We use for for duration – to say how long something lasts. for + period of time I studied the guitar for three years at school.
That house has been empty for six months.
We go away for three weeks every summer.
My boss will be in Italy for the next ten days.
To measure duration up to the present, we use a present perfect tense (see present perfect 6: present perfect or present?), not a present tense.
I’ve known her for a long time, (NOT I know her for a long time.)
We’ve lived here for 20 years, (NOT We tive here for 20 years.)
A present tense with for refers to duration into the future. Compare:
How long are you here for? (= Until when …?)
How long have you been here for? (= Since when …?)
We can often leave out for in an informal style, especially with How long …? And for is not usually used before all.
How long have you been waiting (for)?
We’ve been here (for) six weeks. I’ve had a headache all day.
2 for
and since with perfect tenses: the difference
For and since can both be used with a present perfect to talk about duration up to the present. They are not the same. Compare:
for + period
I’ve known her for three days, (NOT .. .-si-rwe-tkree days.)
It’s been rain ing for weeks.
since
+ starting point
I’ve known her since Tuesday.
It’s been raining since the beginning of the month.
With a past perfect, for and since refer to duration up to a particular past moment.
She’d been working there for a long time, (NOT … since a long time.)
She’d been working there since 1988.
3 in
after negatives and superlatives (AmE)
After negatives and superlatives, in can be used to talk about duration. This is especially common in American English.
I haven’t seen him for/in months.
It was the worst storm for/in ten years.
4 from and since
From and since give the starting points of actions, events or states: they say when things begin or began.
from/since + starting point
I’ll be here from three o’clock onwards.
I work from nine to five.
From now on, I’m going to go running every day.
From his earliest childhood he loved music.
I’ve been waiting since six o’clock.
I’ve known her since January.
We use since (with a perfect tense) especially when we measure duration from a starting point up to the present, or up to a past time that we are talking about.
I’ve been working since six o’clock, and I’m getting tired, (NOT I’ve been working from six o’clock…)
I had been working since six o’clock, and I was getting tired.
From
is used in other cases.
The shop was open from eight in the morning, but the boss didn’t arrive till ten. (NOT The shop was-open since eight…)
I’ll be at home from Tuesday morning (on), (NOT … since-Ttiesday morning.)
From
is sometimes possible with a present perfect, especially in expressions that mean ‘right from the start’.
She’s been like that from her childhood, (OR … since her childhood.) From/Since the moment they were married, they’ve quarrelled.
From/Since the dawn of civilisation, people have made war.
For from … to and from .. . until, see until.
For more about tenses with since, see since: tenses.
For since meaning ‘as’ or ‘because’, see as, because, since and for.
For more information consult a good dictionary like Langman, Oxford, Merriam Webster, or Collins.