英语语法精讲：形容词从句的位置
在《容易犯错的形容词从句》一文里，知道形容词从句总是跟在被修饰的名词(即先行词)后面。例如：① Any change which causes the formation of new matters is a chemical
change.(在主句主语的名词之后)
② Plastics is an important material which is widely used in
industry.(在主句补足语名词之后)
③ It has certain features that are easily recognised.(在主句宾语名词之后)
在下列情况下，形容词从句和所修饰的名词隔开：
㈠被介词短语隔开，如：
④ Magnets work through lines of force that extend between the two ends of
the magnet.
⑤ A molecule may be defined as the smallest particle of matter that can
exist without changing its nature.
④里的形容词从句和先行词“lines”被介词短语“of force” 分离。⑤里的却被另一个介词短语“of matter”隔开。
㈡被分词短语隔开，如：
⑥ There is no method known to medical science today that can effectively
cure cancer.
⑥里的形容词从句和先行词“method”之间被过去分词短语“ known to medical science today”隔开。
上述两种隔离情况可以理解，也被接受。
另外还有一种分隔情况，也偶尔见到，特别在科技英语中，但这种离异法，值得商榷。
例如：
⑦ Several other ideas came along that enabled engineers to design still
smaller units.
⑧ Ninety-six substances are known which chemists consider to be
elements.
⑦和⑧里的形容词从句和先行词“ideas”及“substances”之间都被主句的谓语动词“came along”和“are
known”分开。
这类的分隔情况，多在主句谓语动词是被动语态(the passive voice)时才出现，如例⑧，但谓语动词是主动语态(the active
voice)的话，也可以，如例⑦，只是数量少些。
为什么要把形容词从句常见的位置和先行词分开呢?主要原因是：先行词所在的主句较短，而修饰先行词的形容词从句则很长。为了平衡主句和从句，才采用这方法。虽然如此，但它和一般的形容词从句的位置有很多抵触，恐怕引起混乱。
为了减少不必要的麻烦，最好改用别的句式。其中一个方法是将形容词从句改为另外一个独立的简单句(如例⑨&╆);另一个办法是采用并列句(如例⑩&╇)：
⑨ Several other ideas came along. Such ideas /They enabled engineers to
design still small units.
⑩ Several other ideas came along and these ideas enabled engineers to
design still small units.
╆ Ninety-six substances are known. Chemists consider them to be
elements.
╇ Ninety-six substances are known and chemists consider them to be
elements.
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