My sister / A sister of mine

Question

Are both of these phrases grammatically correct?
"my sister" and "a sister of mine".

Eg. She is my sister. vs. She is a sister of mine.

Is there any difference between the two noun phrases?
In use are they freely interchangeable in any sentence?

Thanks very much,

-A

Mister Micawber · Accepted Answer

ucamAre both of these phrases grammatically correct? "my sister" and "a sister of mine".

Yes.

ucam She is my sister. vs. She is a sister of mine.Is there any difference between the two noun phrases?

Yes: the second sentence implies that you have more than one sister, but the first one does not.

Sundarnaz · Answer

ucamAre both of these phrases grammatically correct?

Yes. But

ucam
She is a sister of mine.
is unnatural. They never say this in this way. They say:

ucamShe is my sister.

You, probably, can use 'a sister of mine' as: A sister of mine is teacher. But, again, the most common is 'one of my sisters is a teacher.'

Hope this helps.

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