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I thought únsure'and not sure were synonymous.

I often see 'not sure' used, but shouldn't we avoid the negated version when we have an alternative? Or is there a good reason why we use 'not sure' instead? It is the same deal with únnecessary and not necessary.

Thanks
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Offhand, I suppose it depends on the surrounding structure.

Are you going to class today?
I'm not sure.
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I'm unsure I can live up to those expectations or I'm not sure I can live up to those expectations. Which of these sounds correct ?
zany navyI'm not sure I can live up to those expectations. Which of these sounds correct ?

This one.

CJ

I associate 'unsure' with a lack of confidence and 'not sure' with a lack of knowledge.

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