How does じゃないか modify hortative in this case?


So far, I have always considered じゃないか to be a tag question meaning "...isn't
it?" with varying nuances depending on context. However, I have seen hortative
+ じゃないか recently, in this short dialog (A and B are dining together):

A:「さ、戻ろう。君のせきが...」  
B:「そんなもん、なんでもないって。」  
A:「さ、いこう。しかし、そのまえに、メドックをもう一本飲もうじゃないか。」  
(メドック is Médoc, a kind of French wine)

I suspect that this じゃないか turns the sentence into some sort of negative
hortative ("won't we drink?") kind of like saying いきませんか？ However, I'm not
sure how exactly じゃないか modifies this sentence. Does strengthen B's
encouragement? Does it have a sense of "urgency" ("we really should have one
more Médoc) or does it the opposite, "softening" the sentence?




This じゃないか denotes a suggestion, "Won't we (drink) ～?", "Shall we ～?" or more
casually, "Why don't you ～?"

While this is common in novels, this sounds a bit pompous or overly classy,
and is rarely heard in reality.

Since じゃ is colloquialism for では, naturally ～ではないか also exists:

> もう一本飲もうではないか。

Basically I expect to hear a sentence like this only from fictional noble
people, historical politicians making a public speech, or such.

