1.Had后面一般加动词的过去分词（表示过去完成时，即“过去的过去”，过去已经发生过的事）；

2.也有You had better do的用法，不过这种用法一般缩写成Youd better do；

3.可以是“have sb do”或“have sth done”的过去式，前者表示“让某人做某事”“对某物做某事”。

扩展资料

She'll have had the results by now.

她现在应该知道结果了。

We had a day out in the country.

我们在乡下玩了一天。

He had to go to the hospital for treatment.

他不得不去医院接受治疗。

Had I known that I would never have come.

要是早知道，我绝不会来的。