"In" or "for" with "a long time"?

Hi, Rashad, and welcome to the G.E,

@Rashad posted:

witch one is correct ?

we haven't seen him in a long time.

we haven't seen him for a long time.

So I had this discussion with my professor about which one of them is correct, and he said "for" is the correct usage and "in" is wrong. but I'm 90% sure that they are both correct in this context. So I need a clear answer with detailed explanation about this question and please provide me with references so I can prove him wrong. Thanks.

Yes, both are grammatically correct. The first one works much better in American English. See here:

https://thegrammarexchange.inf...with-for-a-long-time

@Rashad posted:

So I need a clear answer with detailed explanation about this question and please provide me with references so I can prove him wrong.

Hello, Rashad, and welcome to the Grammar Exchange.

I agree with Ahmed and the early G.E. post to which he has given a link. Both of your sentences are correct. I myself prefer the sentence with "in."

As I see it, the difference is that the sentence with "in" says that no instances of seeing him have occurred in that time, whereas the sentence with "for" says that the period of your not seeing him has had a long duration.

On page 539 of A Comprehensive Grammar of the English Language (Quirk Greenbaum, Leech, and Svartvik; Longman, 1985), there is the following quote:

Quote:

"Indefinite or long backward span can be expressed by for ages or <esp AmE> in ages:

She hasn't been here {for/in} ages."

Thank you very much, both of you. That was very helpful. @ahmed_btm @David, Moderator