expression
Sentence-ending expression seeking agreement or confirmation, similar to a tag question. Often used when the speaker expects the listener to agree.
これ、美味しいではないか。
This is delicious, isn't it?
彼はもう帰ったではないか。
He already went home, didn't he?
expression
let's ...; why don't we ...; shouldn't we ...
Follows the volitional form of a verb to make a suggestion or invitation. Softer than a direct command.
そろそろ行こうではないか。
Why don't we get going?
一緒に食べようではないか。
Let's eat together, shall we?