“ I'm confused about sentences like this:
We were good friends. We had known each other for years.
Could I say in this situation: We didn't know each other for years? ”
I agree with you that this is "pure," a "classic," so to speak. Nevertheless, something has gone haywire (awry).
The first sentence sets it up by using simple past tense. It doesn't specifically say that you are no longer friends, or that the person has died.
But if we had wished to express that we are still friends (or still know each other), we'd have used the present simple, followed by the present perfect: "We
are good friends. We
have known each other for years."
Therefore we assume the friendship has terminated. It's an assumed event in the simple past.
Hmmm. I can see the possibility for a misunderstanding here.
The past tense point in time is not expressed as a point. It's only implied. "We
were good friends." Because of our understanding of the context, we assume the friendship lasted for a period of time in the past and was then terminated by something - an event, or a non-event - which is not expressed here. Perhaps you merely lost touch.
We have our critical point in/of time in the simple past - the implied end of the period when we were good friends.
We now use the past perfect to make a second statement, whose time frame is prior to the
end of the "good friends" period.
"We had known each other for years."
The time frames in
this case overlap. "We were good friends." "We had known each other for years." How do we reconcile this with the notion that the past perfect expression must
precede the simple past expression? Enter the theoretical (or implied) end of the friendship. "We were good friends" conveys two meanings to us: a period of friendship, and an end. "We had known each other for years" precedes the "end."
Your optional statement, "We didn't know each other for years," must be rejected because of our knowledge of the words being used, and the context.
(1) Before we ever met, we didn't know each other for years. This is obviously a true statement, but we reject it because of common sense. Such a thought wouldn't follow from the previous sentence.
If your reasoning is:
the past perfect refers to a time prior to a simple past statement. Therefore it refers to the time before we were friends. I didn't know him. This would be understandable. But again, we must reject it because of common sense.
(2) Your negative optional sentence doesn't follow from the first sentence in your example, "We were good friends." It's grammatical and logical, but it's not idiomatic as a complete thought (the two sentences together.) It doesn't pass the common sense test.
Expressions like "being friends" and "knowing each other" don't necessarily imply a definite ending point in time, as would expressions like, "I passed my driving test," and "I cleaned the house." I guess that's why we must keep "common sense" in mind.