Japanese by Example
Learning through examples in manga

It's not the case with 〜ではあるまいし

〜ではあるまいし expresses a cause or reason. It follows a noun or phrase, and is used to say “Because it is not ~” or “Because you are not ~”.

In the case of expressing a reason, a criticism, warning, advice, or an order may follow after し. However, it’s often the case that the portion after し is omitted.

When following a verb, ん or わけ may appear before で.

The colloquial counterpart is 〜じゃあるまいし.

Further reading


からかい上手の高木さん » Volume 8 » Page 122
名探偵コナン » Volume 3 » Page 147
名探偵コナン » Volume 1 » Page 61