Break down the phrase "[失礼]{しつれい}しなければならないんです"


I've just heard the phrase [失礼]{しつれい}しなければならないんです (shitsurei shinakereba
naranaindesu) used as _Excuse me, I have to leave_. The explanation said it
literally translates to _If I don't leave, it won't do_ , but I need help on
breaking it down precisely.

What does each word mean and how does the grammar work here?




> 失礼{しつれい}しなければならない

失礼 (shitsurei) is "rudeness".

失礼する (shitsurei suru) is "to be rude"

失礼しない (shitsurei shinai) is the negation "to not be rude".

失礼しなければ (shitsurei shinakereba) is a conditional form of the above "If I am
not rude"

失礼しなければならない (shitsurei shinakereba naranai) I'm now sure how to break down
ならない meaningfully but in this context it kind of means "It's no good".

So literally the whole thing means "If I'm not rude then it's no good". Really
you should think of なければならない (nakerebanaranai) as a unit in its own right.
This attaches to the negative form of the predicate and means "must do"/"have
to do" etc, which is the logical implication of the expansion "If I don't do,
then it's no good".

Overall then, the sentence means "I have to be rude", which is what you might
say if you were leaving.




> 失礼{しつれい}しなければならない

失礼 (shitsurei) is "rudeness".

失礼する (shitsurei suru) is "to be rude"

失礼しない (shitsurei shinai) is the negation "to not be rude".

失礼しなければ (shitsurei shinakereba) is a conditional form of the above "If I am
not rude"

失礼しなければならない (shitsurei shinakereba naranai) I'm now sure how to break down
ならない meaningfully but in this context it kind of means "It's no good".

So literally the whole thing means "If I'm not rude then it's no good". Really
you should think of なければならない (nakerebanaranai) as a unit in its own right.
This attaches to the negative form of the predicate and means "must do"/"have
to do" etc, which is the logical implication of the expansion "If I don't do,
then it's no good".

Overall then, the sentence means "I have to be rude", which is what you might
say if you were leaving.

