② 有时省略if后提前的had不是助动词：

Had I time,I would come. 假若我有时间，我会来的。(=If I had time...)省略主语和动词be

若主从句主语一致，且谓语部分包含有动词be，通常可将主语和动词be省略：

If repaired earlier,the tractor would not have broken down.

要是早点儿修一下，拖拉机就不会抛锚了。(=If it had been repaired earlier...)

省略"it+be"

If necessary,I would send more farmhands to help you.如果需要的话，我会派更多的人去帮你。(=If it was necessary,...)

省略条件从句

这样的省略通常需要借助一定的上下文，即省略条件从句后，所剩下的主句的意思在一定的上下文中意思是清楚的：I might see her personally. It would be better. 我可以亲自去看她，这样好一些。(=If I saw her personally,it would be better.)

含蓄条件句中

(1) 条件暗含在短语中。如：

We didn't know his telephone number; otherwise we would have telephoned him.

我们不知道他的电话号码，否则我们就会给他打电话。（暗含条件是otherwise）

Without your help,we wouldn't have achieved so much.

没有你的帮助，我们不可能取得这么大的成绩。

（暗含条件是介词短语without your help）

But for your help,I would not have succeeded in the experiment.

如果没有你的帮助，我的实验就不会成功。（暗含条件是but for your help）

It would cause great trouble not to lubricate the bearing immediately.

不立即润滑轴承就会引起很大的故障。

（暗含条件是not to lubricate the bearing immediately）

(2) 条件暗含在上下文中。如：

I would not have done it that way.我是不会那么做的。（可能暗含if I were you）

I was busy that day. Otherwise I would have come to help you.

我那天很忙。否则我会来帮你的。（可能暗含if I hadn't been so busy.）

You might come to join us in the discussion.你可以参加我们的讨论if you wanted to）

I would have bought the DVD player.我是会买下那台影碟机的。暗含if I had the money

But for the storm,we should have arrived earlier.

要不是碰到暴雨，我们还会早些到。（可能暗含if it had not been for the storm）