华慧考博：如何区分when引导中的定语从句与时间状语从句
在英语语法中，when 作为关系副词时，可引导定语从句，也可引导时间状语从句。很多同学在看到when引导的从句时，便会默认为是时间状语从句，而没有注意有时候，when实际上引导的是定语从句。现在，华慧考博老师重点讲讲如何区分when 是引导的定语从句还是时间状语从句。在此之前，我们首先回顾一下定语从句的三要素，即先行词、关系词、从句，按语法句式，定语从句在整个句子中做定语的成分，被修饰的词称为先行词。而用表示时间的连词连接一个句子作状语，这样的主从复合句称为时间状语从句。
华慧考博
我们先看一下以下两个句子：
- In 2003, when Cambridge University appointed Alison Richard, another former Yale provost, as its vice-chancellor, the university publicly stressed that in her previous job she had overseen “a major strengthening of Yale’s financial position”.（燕山大学 2017年阅读）
- Columbus even sent his brother to England when he failed to obtain support from the Portuguese or Spanish Kings for his proposal that Cathay could be reached by sailing west across the Atlantic.（辽宁大学 2015年阅读）
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我们知道，例句1中的从句为定语从句，修饰前面的时间状语in 2003，而例句2中的从句为时间状语从句，修饰的是动词sent。通过对比，我们可以总结出when 引导的这两种从句有如下四种不同。
- 修饰关系不同，when 引导定语从句时，该词前面必定有表示时间的名词，即前文所述的先行词；而when 引导时间状语从句时，则前面没有表示时间的名词，这是因为when 引导的时间状语从句是用来修饰动词，表示动作或状态发生的时间。
- 从句的位置不同, when 引导定语从句时，只能置于主句的时间名词（即先行词）之后；而when 引导时间状语从句时，从句可以置于主句之后，也可置于主句之前（此时用逗号来分隔主从句），例句2可以改写成: When he failed to obtain support from the Portuguese or Spanish Kings for his proposal that Cathay could be reached by sailing west across the Atlantic, Columbus even sent his brother to England. 而例句1不能这样改写。
- when的作用不同，when 引导定语从句时，指代的是表示时间的先行词，这时when在定语从句中作时间状语，修饰从句的谓语；而when 引导时间状语从句时，when在从句中不充当任何成分，只连接主句和从句。例句1，when指代 in 2003, 作Cambridge University appointed Alison Richard, another former Yale provost, as its vice-chancellor的时间状语，即剑桥大学任命前耶鲁大学教务长艾莉森 理查德 为副校长的时间是2003年；而例句2中的when在从句中没有任何成分。
- when 的翻译不同，when 引导定语从句时，一般可依据从句的时态来翻译，如果从句谓语动词是过去时，when可译为“当时”、“那时”；如果从句谓语动词是将来时，when可译为“到时”、“届时”。而引导状语从句的when，通常都是译成“当......时候”。
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我们再来看几个由when引导的从句，大家试着辨别是定语从句还是时间状语从句。
- Others realize it when they contact biological half-siblings who have the same disorder. (医学统考2013年阅读)（时间状语从句）
- When Barack Obama signed a sweeping set of health reforms into law on March 23rd 2010, he knew it was a historic moment and not just because Joe Biden, the vice-president, whispered into his ear that it was a “big fucking deal.” (广西大学2016年阅读) （时间状语从句）
3. Through product diversification and careful market research, Reebok hopes to avoid the distribution problems Nike came several years ago, when Nike misjudged the strength of the aerobics shoe craze and was forced to unload huge inventories of running shoes through discount stores. (首都经贸大学2015年阅读) （定语从句）4. The Agricultural Revolution that began in seventeenth-century England radically increased the amount of food that could be grown on an acre of land, and the same happened in the 1960s and 1970s, when fertilizer and hybridized seeds arrived in India and Mexico. (中科院2015年阅读)（定语从句）
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