could have PP

推量

I could be wrong. 私は間違っているかもしれない。

I could have been wrong. 私は間違っていたかもしれない。

仮定

I could go to Japan if I had a holiday. 休暇があれば日本に行けるのに。（実際には休暇がない）

I could have gone to Japan if I had had a holiday. 休暇があったなら日本に行くことができたのに。（実際に休暇がなかった）

 (仮定　少し後悔の念　～できただろう　 過去の推量　～でしょう（could+have+PP）

I wish I could have

Couldn't you have gotten something...

Couldn't you have gotten something a bit more comfortable?

I could have study English more