《实用英语语法》(张道真编著,外研社,1995,p.96)说:
“which 代表事物,在从句中可以作主语或宾语……that 代表事物的时候更多一些,也可代表人,在从句中可以作主语、宾语或表语。”
据此我得出如下结论：
当中心词为表物的名词,而关系代词在从句中作主语或宾语时,which 和 that 是完全可以互换的。
《实用英语语法》，作为一部中级英语语法书，对 which 和 that 所作的陈述是恰当的。你如果是一位英语初学者的话，那你所做的结论是很实用的。但是，你如果具有较高的英语水平，则应查找其他资料，进一步弄清 which 和 that 的惯用法问题。下面提供一些参考资料。通常使用 that 的场合：
A. 当先行词是 all, anything, something, everything, nothing, little, much, none, one 时, 人们大都喜欢使用 that 或省略充当宾语的 that(即零关系代词):
-
All is well that ends well. 结果好,一切都好。
-
Have you everything that you need? (Eckersley) 你是否(拥)有你所需要的一切东西?
-
She has everything (that) a woman could wish for. (GPU) 她拥有女人想获得的一切。
-
I'll tell you something that you didn't know before. (EED) 我要告诉你你从前不知道的一些事情。
-
I never have taken anything that didn't belong to me. (Galsworthy) 我从不去获取不属于我的东西。
-
Much that has been said tonight will soon be forgotten. (CGEL) 今天晚上说的许多话很快就会忘记。
-
There was little that interested him at the motor show. 汽车展销会上引起他兴趣的东西极少。
-
The government has promised to do all that lies in its power to help. 政府答应尽全力进行援助。
B. 当被修饰的名词(即先行词)有 only, all, any, few, little, no, one of 等修饰语时,人们通常喜欢用 that 或者省略 that(当 that 作宾语时):
The only thing that impresses me is her directness. 唯一给我留下深刻印象的就是她的直率。
C. 当先行词受最高级形容词、顺序数词、last、next修饰时，通常使用that或零形式：
They eat the finest food that is available. (GCE) 他们吃所能买到的最好的食品。
D. 当先行词既含表人的名词又含表物的名词时,这时只能使用 that:
The generals complained that the Defence Department had not sent the extra men and equipment that they needed. (CGEL) 将军们抱怨国防部没有给增派他们所需要的人员和设备。