一、省略连词if

有时可将条件从句的连词if省略，但此时应用倒装句型，即将从句中的were, should, had 等提到句首：

Were I Tom, I would refuse. 如果我是汤姆，我会拒绝。

I will go, should it be necessary. 假若有必要，我会去的。

Had it not been for the bad weather we would have arrived in time. 若不是天气坏，我们就准时到达了。

【注】① 若条件从句为否定句，否定词not应置于主语之后，而不能与were, should, had 等缩略成Weren’t, Shouldn’t, Hadn’t而置于句首。

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…)

二、省略条件句的主语和其后的动词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…)

三、省略“it+be”

If necessary, I would send more farm-hands to help you. 如果需要的话我会派更多的民工去帮你。(=If it was necessary, I would…)

四、省略整个条件从句

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.)