Nuance of かと思えば in this context

Question

敷石ぐらいの大きいな革製本、シルクの表紙で切手くらいの大きさの本もあり、奇妙な記号ばかりの本があるかと思えば、何にも書いてない本もあった。
There were leather bound books as big as paving slabs, silk covered books the size of postage stamps. There were books with nothing but weird symbols ???? There were also books with nothing written in them.

It seems that Xがあるかと思えばYもある means 'There is not only X but also Y'. What nuance does this construct have? In what situations would it be used? How would it differ from だけではなく, for example?

I'm guessing from 思えば that it invokes some element of surprise/wonder?

Answer 1

Aかと思えばB expresses a psychological sequence of observations. This is a common pattern used to express that this person noticed one thing after another in a short period of time ("Oh it's A, and oh, it's B, too!"). The same construction is used to describe one event actually happened right after another, for example, 彼は部屋に入ってきたかと思えばすぐに出ていった (He left the room right after (I noticed) he entered it).

AだけではなくB simply means "not only A but also B". This construction puts emphasis on the B part (B is usually more surprising/relevant/important). On the other hand, in Aかと思えばB, B is something that happened (or was recognized) right after A.