What does ～ないことはない mean?

Question

I have looked up the '～ないことはない' grammar and it says it means either 'can' or 'is not impossible to' Link to grammar site. I see that it's a double negative.

However, I have this sentence that I've had trouble fitting it to.

まあ アイデア出した俺にも責任はないことはないか

I understand the parts. He came up with the idea, and he feels ... that he 'can' be responsible? In English, it seems like it might be 'should' be responsible, or at least 'it's not the case that I shouldn't be responsible'. But then 'nai koto ha nai' starts to become 'isn't the case that', and that starts to feel more like 'wake ja nai'. I suppose the first step would be to have a good translation of this line, which I don't have.

So, in short, I'm having trouble understanding this question. And if it does translate to 'isn't the case that', then I would appreciate someone explaining the main differences between 'nai koto ha nai' and 'wake ja nai'.

Thanks!

Answer 1

'～ないことはない' is a kind of softener which indicates that the speaker believes something has a lower probability of possibility or a smaller degree than in other phrases like たぶん or かもしれない, for example.

With ～ないことはない, the first ない is softened by the second ない. So 責任はないこと ('I have no responsibility') is softened with the additional ない (literally 'it's not that I have no responsibility'). This produces a phrase where the speaker is still expressing low probability but is also admitting that it isn't out of the question or might be partly true at least. More context on what the speaker is talking about in your examples would be helpful, but anyway I would translate it as something like this (depending on the context):

まあアイデア出した俺にも責任はないことはないか.

I guess I'm the one who suggested the idea, so I suppose it could partly be my fault too.　　

He's allowing for the possibility that he is responsible, but is also distancing himself from it somewhat by using ～ないことはない to reduce the degree of responsibility that can be assigned to him.

Answer 2

ないことはない　is definitely putting some distance between the cause/effect, or the possibility of something happening. It's similar to "(You) can't say it will never happen, but..." or "It's not impossible that..."

I would say that the use of this phrase in this case can be shown in the difference between these two English sentences.

Because I mentioned the idea, it's my responsibility. vs. Because I mentioned the idea, I can't say I bear no responsibility.