if引导的表语从句

The only way she could get this injury is if someone shook her,and they would have

to shake her hard.之前向老师咨询过if引导表语从句的问题，今天碰巧遇见这句话，由于不太确定这句话是不是能像http://ask.yygrammar.com/q-43905.html里那样去讲解，所以想确定下这是if引导的表语从句吗？这句话是不是不规范？

你说你没见过if 从句作表语的，这里你又见到了。所以if从句坐落于be之后的语言现象是存在的，问题在于怎么样理解和讲解这种现象。

回答你这个问题之前，大家先回顾一下because从句坐落于be之后的句子。

because从句坐落于be之后，主语可以是两种状况。

1 主语为指示代词或人称代词it，指代前面提到过的一件事情。比如：

You lost your bike again. That/It was because you were too careless.

汉语翻译时，翻译为：这是由于你太不小心了。好像是个系表结构。 但从逻辑上剖析，that/it指的是your losing the bike again这件事，这件事做主语，was为不及物动词，意为happened/took place。because从句仍然是缘由状语从句，而不是表语从句。 该句等于：

That/It happened because you were too careless.

2 主语为reason，表语说明reason是什么时，本应该用that从句，而大家误用了because。比如：

You lost your bike again. The reason was that/because you were too careless.

The reason you lost your bike again was that/because you were too careless.

托福考试明确指出because的用法为错误，要把because改为that。由于这里是确认性表语，A=B，B=A，不该用because 引导表语从句。但讲母语的人也会犯这种逻辑错误，因此这种语法错误的句子作为非正式语体而被皱着眉头同意。严谨的作者会防止此类句子的。

目前回到你的句子。

The only way she could get this injury is if someone shook her,and they would have

to shake her hard.

从逻辑上讲，这个句子要说明唯一的方法是什么，那样表语就是唯一的方法。这里也需要一个名词性从句表示这个方法。即主语A=表语B，表语B也=主语A。此时应该用that引导名词性表语从句：

The only way she could get this injury isthat someone shook her,and they would have

to shake her hard.

大家可以把主语和表语的功能互换，让that从句作主语，the only way作表语，句子依旧成立：

That someone shook her, and they would have to shake her hard, is the only way she could get this injury.

由此可知，这个句子用if是一种失误，在本该用名词性表语的地方，误用了状语从句。就好似reason作主语，本该用that引导名词性从句，而误用了because从句的情形是一样的。但因为说母语的人确实有人这么用，大家也不可以说这种使用方法完全错误，只不过不够规范而已。把if改为that，就是规范的英语句子了。

另外，黎老师觉得把if 改为whether是不可以的。if在此是假如的意思，不是是不是的意思。改为whether句子是不通的。