What it means
ないことはない is a double-negative pattern meaning that something is not completely impossible, false, or excluded. It often expresses a qualified possibility or concession, such as “it is not that...” or “it is not impossible that...,” rather than a strong, definite assertion. It attaches to a verb in its nai-form, to a noun or na-adjective with でない, and to an i-adjective with くない.
Usage note
ないことはない often sounds cautious or indirect and can imply that the speaker is only partly agreeing. It should not automatically be translated as a confident positive statement.
How to use it
彼が医者でないことはありません。
It is not that he is not a doctor.
この方法が便利でないことはありません。
It is not that this method is not convenient.
この料理が辛くないことはありません。
It is not that this dish is not spicy.
私が会議に行かないことはありません。
It is not that I do not go to the meeting.
彼が医者でないことはない。
It is not that he is not a doctor.
この方法が便利でないことはない。
It is not that this method is not convenient.
この料理が辛くないことはない。
It is not that this dish is not spicy.
私が会議に行かないことはない。
It is not that I do not go to the meeting.