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As I understand, they are both very close in terms of meaning.

E.g.

私は歌を歌えないわけではないが、人前で歌うのは恥ずかしい。
私は歌を歌えないことはないが、人前で歌うのは恥ずかしい。

Both sentences would mean: "It's not that I cannot sing, it's just that I get embarrassed in front of others."

I'm pretty sure there is a slight difference in nuance, that I can't quite grasp yet.

Is it a matter of opposing the belief of someone that you can't? (while the other is plainly a statement?)

naruto
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悪戯猫
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2 Answers2

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There is very little difference, and they are interchangeable most of the time. Still, I feel the speaker is more aware of the previous context when わけではない is used. That is, a sentence using わけではない tends to have a nuance of "that is not to say", "that doesn't mean" or "I'm not saying". ことはない is a relatively "plain" double-negative sentence.

naruto
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Not sure if this is what you are looking for, but -タ form seems to behave differently for the two constructions. As I see it, なかったことはない coincides with another construction -たことがある, which takes precedence. なかったわけではない doesn't have the same problem.

私は歌が歌えなかったことはないが、人前で歌うのは恥ずかしかった。

Most people will read this as "I have never been unable to sing" (="I always could"). The other interpretation ("It's not that I couldn't sing"="I could to some extent") might not be impossible, but it would be much harder to read that way.

Whereas, the same doesn't happen when you change ないわけではない to なかったわけではない.

私は歌が歌えなかったわけではないが、人前で歌うのは恥ずかしかった。

The only difference from the original sentence is that it describes a past event.

Yusuke Matsubara
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  • Thanks for the Insight! Indeed, as @naruto mentioned before, ことはない is a plain negation so whether ない・なかった comes before, it is a simple "plain" double-negation. To my estimation so far it seems like わけではない is more close to: "It's not that...". It's as if you are explaining or disagreeing with the other person's guess/estimation. In that case the Past-Sentence example puts things in their place clearly. – 悪戯猫 Sep 27 '22 at 18:47
  • As I see it, the main issue in what I argued is a conflict with another construction -たことがある. I edited my answer to clarify. – Yusuke Matsubara Sep 28 '22 at 09:25