原书 PDF 第 1263—1264 页
在张道真《实用英语语法》和章振邦等编《新编英语语法》中只指出了 the reason why 的用法：That is the reason (why) I did it. 这就是我这样做的原因。是不是只有 why 才能引导 the reason 的定语从句？
除了 why 之外, that 也能引导 the reason 的定语从句, 而且是规定语法学派所倡导的用法。例如:
The reason (that) they didn't go to see the house is that they prefer to live in an apartment. (CGEL) 他们没去看房子的原因是他们宁愿住在公寓里。
[参见 that(adv.)²]
the reason that 与 the reason why 到底哪一个是规范用法？
规定语法学家反对使用 the reason why 来代替 the reason that。但事实上，the reason why 不仅普遍用于文学著作和语法著作，而且也为各类考试所认可。这说明这种用法不仅受到人们的欢迎，而且已进入标准英语。请考察下面的例句：
There was no very definite reason why she should do so. (Dreiser) 她为什么这样做没有非常确定的原因。
That is no reason why you should leave. (Bennet) 这不是你要走的原因。
The reason why we are late is that our car did not come. (Hill) 我们来晚的原因是我们的汽车没来。
The reason ____ I'm writing is to tell you about a party on Saturday. A. because B. why C. for D. as(Nelson, 250A)
The reason why he died was lack of medical care. (LCAD) 他死的原因是缺乏医疗。
The reason why he was driving so fast was that he was late for an important meeting. 他车开得这么快,是因为他要参加一个重要的会议,而他却要迟到了。
The reason why the pound is declining in value against the dollar is that American interest rates are being kept so high. (RWRT) 英镑对美元的比价在下跌的原因, 是美国保持着很高的利率。
I think that was the reason ____ our football team lost the game. A. that B. which C. how D. why
《中学英语答疑析难》(高三分册)(吉林教育出版社,p.21)对上题作了如下解答:
“此题的正确答案为 D。why 引导的是定语从句，先行词是 the reason, why 是关系副词在从句中作原因状语；that 是关系代词，在从句中常充当名词（代词）所能充当的成分。而如果把 that 看成是连词的话，它在从句中不作任何成分，但 the reason 后一般不接同位语从句，所以不能选 A。” 您也认为不能选 A 吗？
从试题本身以及解答者的解答可以看出,the reason 不能接 that 的说法是我国英语教学上的一个误区,应当引起我们的注意。实际上,the reason why 和 the reason that 的用法都是正确的 (that 可以用作关系副词),见 the reason why/that , that(adv.) , appositive clause or attributive clause。
《无敌英语语法》(高中版)(海豚出版社,p.270)说:
“一般来讲在定语从句中只要先行词是 the reason, 它的关系副词就是 why, 但是在口语中, 也和 when 一样, 关系副词 why 也常被 that 代替, 也可以省略。” the reason why 和 the reason that 究竟哪个是口语用法?
the reason why 为口语用法(非正式语体用法), 见 the reason why/that , that(adv.) 。the reason why/that
The reason why we use oxen is that we can't afford to buy a tractor. 请问 why we use oxen 是什么类型的从句？
它是定语从句，见 appositive clause or attributive clause。
The reason Frank is going to Arizona is that he needs a dry climate. 请问上句中的 Frank is going to Arizona 是什么从句？
Can you think of any other reason he might be convinced you're guilty? (Dan Brown, The Da Vinci Code) 你能找出他为你定罪的理由吗？(《达·芬奇密码》)
应把 Frank is going to Arizona 看作是省略了关系副词 why 或 that 的定语从句，因为在非正式语体中，关系副词 why 或 that 是可以省略的。参见 appositive clause or attributive clause、the reason why/that¹–⁵。