You use this phrase when you feel you must do something. It means you have no other choice. You feel a strong need to do it.
Verb [ない-form] + わけにはいかないPrimary
You use this phrase when you feel you must do something. It means you have no other choice. You feel a strong need to do it.
部長のパーティーだから、参加しないわけにはいかないんだ。
Since it's the department head's party, I have no choice but to attend.
親友が困っていたから、助けないわけにはいかなかった。
My best friend was in trouble, so I couldn't not help them; I had to help.
お客様からのご依頼ですので、お受けしないわけにはいきません。
As this is a request from a client, we have no choice but to accept it.
手伝わないわけにはいかないからといって、自分の仕事を疎かにしてはいけない。
Just because you feel you must help doesn't mean you should neglect your own work.
熱が38度もあるが、大事な試験なので休まないわけにはいかず、結局会場に向かった。
I had a 38-degree fever, but since it was an important exam, I couldn't not take it, and ended up heading to the venue.
This grammar shows you must do something. It is not a strict rule. It is more like a strong feeling inside you. You might not want to do it. But you feel you have to. It is like a push from your heart or from others.
This is different from 'wake ni wa ikanai'. That means you cannot do something. This means you must do something. For example, 'I promised, so I must go'. This is not 'I'm sick, so I cannot go'.
Watch out: This is different from "〜ないわけではない". That phrase means "it's not that I don't..." This phrase means "I must do it." For example, "食べないわけにはいかない" means "I must eat." But "食べないわけではない" means "It's not that I won't eat."
Don't use this when you tell others what they must do. For example, don't say, "You must go." This sounds rude. It is okay to ask, "Must you go?" Or you can talk about what someone else feels they must do.
Contrasts with(2)
More formal alternatives(1)
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