在英文写作中常常需要用到连接词进行句子之间的过渡，但是有些连接词的用法很相似，因此在使用过程中会容易出错。因此本文就“which”和“that”的用法进行比较，区分这两者在写作中的用法。
“That”起到的是“限制”的作用，而“Which”则是用来“描述”的。
这当中有两个原则
如果一个分句，就算从句子中去掉也不会影响句子的完整性，则用“which”引导; 如果这个分句在句子中起到关键作用，那么就用“that”。
“Which”分句通常都是用逗号隔开的；“That”分句不可以用逗号隔开。
用普通的例子来表示，就是：
The car that I drive is a red Toyota Prius.
My car, which is a Toyota Prius, gets 50 miles per gallon.
The car that I drive, which is a red Toyota Prius, gets 50 miles per gallon.
在学术写作中：
Tamoxifen, which is a so-called anti-estrogen, is the most appropriate drug for this patient.
他莫昔芬，就是所谓的抗雌激素，是最适合这类病人的药物。
在这句话中，去掉“which is a so-called anti-estrogen”，句子的意思变成“他莫昔芬是最适合这种病人的药物”。句子的大体意思没变。且如果没有逗号，这句话读起来不通顺。
The drug that is most appropriate for this patient is tamoxifen.
最适合这类病人的药是他莫昔芬。
在这句话中，如果去掉“that is most appropriate for this patient”，句子大意变为“这种药是他莫昔芬。”句子无法表达出原本的意思，且如果用逗号隔开变成“The drug, that is most appropriate for this patient, is tamoxifen.”也不符合阅读习惯。
而常见的错误写法是：
The drug which we used to block redox signaling was tempol.
这句话的意思是“我们用来阻断氧化还原信号的药物是tempol。”其主要目的是表达该药物“阻断氧化还原信号”这一作用，因此“we used to block redox signaling”是不可省略的。所以该分句应该用“that”引导。
The drug that we used to block redox signaling was tempol.
以下是同一个句子分别用“that”和“which”引导的例子，可以看出这两个连接词之间的区别是遵循上文提及的原则的。
Rats that are treated with STZ develop diabetes symptoms.
STZ-treated rats, which are totally defective in insulin secretion, are a common model of Type 1 diabetes.
The receptor that is the subject of my NIH grant is the AT2 angiotensin receptor.
The AT2 angiotensin receptor, which is the subject of my NIH grant, is a Gq-coupled receptor.
The receptor that is the subject of my NIH grant, which is the AT2 angiotensin receptor, is a Gq-coupled receptor.
转自学术助航微信公众号，仅作学习交流，如有侵权，请联系本站删除！
