四、限制性和非限制性定语从句

1. 定语从句有限制性和非限制性两种。限制性定语从句是先行词不可缺少的部分，去掉它主句意思往往不明确；非限制性定语从句是先行词的附加说明，去掉了也不会影响主句的意思，它与主句之间通常用逗号分开。例如：
    This is the house which we bought last month. 这是我们上个月买的那幢房子。（限制性）
    The house, which we bought last month, is very nice. 这幢房子很漂亮，是我们上个月买的。（非限制性）
2. 当先行词是专有名词或物主代词和指示代词所修饰时，其后的定语从句通常是非限制性的。例如：
    Charles Smith, who was my former teacher, retired last year. 查理?史密斯去年退休了，他曾经是我的老师。
    My house, which I bought last year, has got a lovely garden. 我去年买的的那幢房子带着个漂亮的花园。
　　This novel, which I have read three times, is very touching. 这本小说很动人，我已经读了三遍。
3. 非限制性定语从句还能将整个主句作为先行词, 对其进行修饰, 这时从句谓语动词要用第三人称单数。例如：
    He seems not to have grasped what I meant, which greatly upsets me. 他似乎没抓住我的意思，这使我心烦。
    Liquid water changes to vapor, which is called evaporation. 液态水变为蒸汽，这就叫做蒸发。
    说明：关系代词that和关系副词why不能引导非限制性定语从句。
4. 限制性定语从句中只能用that 引导定语从句的情况
    1) 当先行词是everything, anything, nothing (something 除外), all, none, few, little, some等代词时，或当先行词受every, any, all, some, no, little, few, much等代词修饰时。如：
    Have you taken down everything that Mr. Li said?  李老师讲的你都记下来了吗？
    There seems to be nothing that is impossible to him in the world.  对他来说似乎世界上没有什么不可能的事。
    2) 当先行词被序数词修饰时。如：
    The first place that they visited in London was the Big Ben.  在伦敦他们参观的第一个地方是大本钟。
    3) 当先行词被形容词最高级修饰时。如：
    This is the best film that I have ever seen.  这是我看过的最好的电影。
    4) 当先行词被the very, the only修饰时。如：
    This is the very dictionary that I want to buy.  这正是我要买的词典。
    After the fire in his house, the old car is the only thing that he owns.  家里发生了火灾过后，那辆旧车成了他的唯一拥有。
    注意：当先行词指人时，偶尔也可用关系代词who。如：
    Wang Hua is the only person in our school who will attend the meeting.  王华是我校唯一出席会议的人。
    5) 当先行词前面有who, which等疑问代词时。如：
    Who is the man that is standing by the gate?  站在门口的那个人是谁？
    Which is the T-shirt that fits me most?  哪件T恤衫最合我的身？
    6) 当先行词为人与动物或人与物时。如：
    They talked about the persons and things that they remembered at school  他们谈论着他们所能记起的在校时的人和事。
    Look at the man and his donkey that are walking up the street.　瞧瞧那个沿街走来的人和他的毛驴。