Hello, everybody! My student asked me a question: Do native speakers say it in this way?
1) I haven't seen you for a long time.
2) I havn't seen you for long.
3) I haven't seen you for ages.

Can the verb SEE mean an action lasting for a period? (I don't quite think so.) If it doesn't mean an action lasting for a period, how can we use "for a long time" or "for ages"? Many Chinese students say it as 1). Is it right? Why?According to Oxford Dictionary, "for a long time " is usually used in positive sentences,while "for long" is used in questions or negatives. It means the sentences above are ungrammatical. How can we distinguish "for a long time" and "for long"?Can you explain these phenomena? Thanks a lot!
1 and 3 are ok.

In these examples you are not talking about something you have been doing. Rather, you are expressing the gap in time that no action occured. See has the meaning of meet here and it means one time meeting but over many occasions, just like had in the following examples:

I haven't had a hamburger for a long time.

I haven't had a hamburger for ages.

There are a few verbs that we generally don't use in the present continuous: have, see, like, love ...

"for a long time " is usually used in positive sentences Usually is the key word here.

I would say that for a long time is common in negative sentences, but agree that we rarely use it in questions.

I hope that helps.

Hmm... this got me thinking: What is more appropriate: "for" or "in?" Is there a general rule?

So is "I haven't seen you in ages." acceptable as well? "I haven't seen you in a long time." sounds alright to me.

"I haven't seem him for a while." sounds okay but now I'm not so sure about "I haven't seen him in a while."

Oh, and there's that other expression: "I haven't seen you for eons." Makes me wonder as well, where could've this originated from?

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I want to comment on to Mesmaks answer, that here in Azerbaijan I have encountered quite a lot of foreigners using expression "for long" as in the sentence mentioned above. And it seem ok for me.

Regarding to Jeromes comments, want say that using "in" instead of "for" specifically in this case seems wrong to me wrong. I have never heard of it. "for" is one of the special prepositions indicating to the use of perfect tense form.