I have encountered this sentence:
Mitbewohner in WGs müssen aber nicht beste Freunde sein.
Why isn't it like this:
Mitbewohner in WGs müssen aber keine besten Freunde sein.
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Sign up to join this communityI have encountered this sentence:
Mitbewohner in WGs müssen aber nicht beste Freunde sein.
Why isn't it like this:
Mitbewohner in WGs müssen aber keine besten Freunde sein.
There is nothing weird about this. German regularly alternates between these two variant ways of expressing the same:
Ich bin Arzt und nicht Ingenieur, Jim!
Ich bin Arzt und kein Ingenieur, Jim!
Both mean "I'm a doctor, not an engineer, Jim!" and there is very little difference in meaning.
Alternation is a natural phenomenon of language that crops up nearly everywhere. You only notice it when a foreign language has it where your native language doesn't.
I agree that the usage is interchangeable and just a variation. In the first case it could be a nuance of stronger negation, in the second case the emphasis is more on "best friends", more the quality of relationship. In English it is similar to phrases like "they are not best friends" and "they are no best friends".
But in general no one would make up his mind about those nuances of meaning, at least not those with average education.
They mean pretty much the same. Syntactically, nicht negates the verb sein müssen, while keine negates the nominative beste Freunde.
Edit: I've spent some time thinking about my answer and I've came to conclusion I was wrong.
Consider the use of "dürfen" in place of "müssen" and a simple ban like "you are not allowed to bring any alcohol".
"Man darf nicht Alkohol mitbringen" and "Man darf keinen Alkohol mitbringen" mean the same. It must work the same with the negation of "müssen".
Sorry for the confusion and a wrong answer.
Original: The first one reads (for me) as "The flatmates don't really need to be best friends", while the second I'd interpret as "The flatmates aren't allowed to be best friends".