第五章 虚拟语气 条件句（Conditional Sentences)

　　条件句有两种，一种是真实条件句(Sentences of Real Condition)，表示一个可能实现的情况：

　　I'll help him if he asks me.

　　如果他向我提出，我可以帮助他。

　　If she isn't in, leave her a note.

　　如果她不在家，给她留一个条子。

　　另一种是虚拟条件句(Sentences of Unreal Condition)，表示一种纯然假想的情况或实现的可能性不大的情况，这时动词需用特殊形式，称为虚拟语气，虚拟条件句有两种：

　　1.谈过去的情况，动词为：had+过去分词, would have+过去分词

　　If he had asked me, I would have helped him.

　　如果他向我提出了，我就帮助他。(但他没向我提出)

　　If she had left five minutes earlier, she would have caught the train.

　　如果她早五分钟动身，她就赶上火车了。(但动身晚了)

　　2.谈现在或将求情况，动词为：过去式would+动词原型

　　If I had the money, I would travel round the world

　　如果我有钱我将作环球旅行。(但我没有钱)

　　I would help you if I could.

　　如果能我是会帮助你的。(但不可能)

　　动词为be时，多用were这个形式：

　　If I were you, I would accept the job.

　　我要是你我会接受这份工作。

　　有时if可以省略，这时后面要用倒装语序：

　　Had I taken (=If I had taken) your advice, I wouldn't have made that mistake.

　　如果我听了你的劝告，我就不会犯那个错误了。

　　Were I in your position, I would stay.

　　我要是处在你的地位我会留下。

　　条件从句 主句

　　had+过去分词 would have +过去分词

　　条件从句 主句

　　过去式 would +动词原形