7.关系代词but与than的用法

在初级英语阶段，我们知道引导定语从句的关系代词有who，whom，whose，that和which等。到了中高级阶段，这些显然是不够的。还应了解but和than也可以作关系代词的情况，以拓宽知识面，提高语言识别和理解能力。

(1)关系代词but的用法。

but在英语句子中可以作关系代词，引导定语从句。但应特别注意but虽然形式上是肯定的，意义上却是否定的。这正是but和其他关系代词(who，that，which等)的不同之处。

There is no rule in English but has exceptions．

英语中没有无例外的规则。

There is no old habit but may be cured by a strong will-power．

通过强大的意志力没有改不了的旧习惯。

With the introduction of the electronic computer，there is no complicated problem but can be solved in a few hours．

由于引进了电子计算机，没有在几小时内解决不了的复杂问题。

There is no human being but makes mistakes．

没有不犯错误的人。

Not a man but had tears in his eyes．

没有一个人眼睛里不含着眼泪。

but作关系代词时相当于that．．not或who not。上述五例分别相当于:

There is no rule in English that has no exceptions/that has not any exceptions．

There is no old habit that may not be cured by a strong will-power．

With the introduction of the electronic computer，there is no complicated problem that cannot be solved in a few hours．

There is no human being that(who)makes no mistakes/that(who)does not make any mistakes．

Not a man who didn't have tears in his eyes．

(2)关系代词than的用法。

than引导定语从句时，主句中总是含有比较等级，关系代词than在从句中充当句子的主语。

To compensate for his unpleasant experiences in hospital，the man drank a little more than was good for him．(NCE第三册第29课)

为了补偿住院这一段不愉快的经历，那人喝得稍许多了一点。

提示：

在此句中，之所以使用关系代词than，是因为主句中出现了比较等级more(wine)，than在从句中作主语，由于more表示单数意义，所以定语从句的谓语动词用了单数的was。而在下例中谓语动词用了复数的were。He smoked more cigarettes than were normally available．他吸的香烟比他弄到的要多。这里than在语法功能上相当于that/which的功能，但是这里不能改成后者，因为主句中有比较级more。

To understand the situation completely requires more thought than has been given thus far．

要彻底理解这种局势需要作比迄今为止更多的思考。

You spent more money than was intended to be spent．

你花的钱比原计划的要多。

He donated more books than were needed．

他捐赠的书比需要的多。

提示：

可以把than引导的定语从句与that/which引导的定语从句进行对比。

To understand the situation completely requires thought that has been given thus far．

He donated books that were needed．

也可以与as引导的从句进行对比。

She is love by all her students，as is common knowledge．