d[if 節の中で] もし…すれば, できれば‖I'd buy a computer if I could afford it. もしお金の余裕があればコンピュータを買うのですが.

e[S could have done][if 節の帰結節として](もし…であったなら)…できたろうに‖The driver could have avoided the accident if he had been more careful. もっと注意深かったら運転手は事故を避けることができたろうに(＝It would have been possible for the driver to avoid ... ＝The driver couldn't avoid the accident because he was not careful enough.).