虚拟语气的倒装形式

当虚拟条件句中含有were，had，should，could等动词时，可以将if省略，然后将we re，had，should，could 等词移至句首：

1.If he should fail，he would kill himself.

→Should he fail，he would kill himself.

万一失败，他就会自杀。

2.If I were you，I would do it at once.

→Were I you，I would do it at once.

假若我是你，我就会马上做。

3.If I could do it，I would.

→Could I do it，I would.

要是我能做此事，我一定会做。

4.If he had seen you yesterday，he would haveasked you about it.

→Had he seen you yesterday，he would haveasked you about it.

他昨天要是看到了你，他就会问你这事了。

顺便说一句，以上移至句首的had不一定是助动词，如果是实义动词也可倒装：

If he had money，he would buy a car.

→Had he money，he would buy a car.

他要是有钱，他就会买一辆小车。