在雅思寫作中，一般的簡單句會用一個形容詞做定語來修飾一個名詞，但當定語成分太過復雜而不能只用單個形容詞擔當時，就要借助于一個句子來做定語修飾名詞。
像這樣由句子擔當定語，對被修飾的先行詞進行有限定制約，使該詞的含義更具體，更明確，我們稱之為限定性定語從句，下面我們結合例句進行對比學習：
a)I don’t like lazy people(形容詞做定語放在名詞前面).
b)I don’t like the people who never keep their words. 我不喜歡從不遵守諾言的人.
在限定性定語從句中，有兩個比較重要的概念。以b句為例,獨立主句是：I don’t like the people;定語從句為“who never keep their words”，相當于一個形容詞，做定語修飾名詞“the people”， 且從句和主句是由who來連接的。在定語從句中，“the people”被稱為先行詞，指被定語從句所修飾或限制的對象。“who”被稱為關系詞即重復指代先行詞，并在定語從句中充當一定成分的連詞。
從上面的解析不難看出，關系詞在限定性定語從句中很重要，是連接主句和從句的關鍵。關系詞可以分為關系代詞和關系副詞，下面我們一起來進行具體的學習。
I.關系代詞主要有：who, whom, whose, which, that.
A. 當先行詞為人時，可用關系代詞who,whom,whose 和that.
a. 若關系代詞在從句中做主語時，選用 who 或that.
eg：The woman is a responsible teacher who /that is loved by her students.
= The woman is a responsible teacher and she is loved by her students.
b. 若關系代詞在從句中做賓語時，選用 whom(首選),who 或that.
eg: The girl whom we are talking about is a good friend of us.
c. 若關系代詞在從句中做定語,表示人的所有關系時，選用 whose 或of whom.
Eg:I know a friend whose sister is a famous dancer.
= I know a friend. His sister is a famous dancer. (whose 代替了his,指人 friend)
B.當先行詞為物時，可用關系代詞which, that 或whose.
a. 若關系代詞在從句中做主語或賓語時，選用 which 或that.
Eg:These are the trees which / that are destroyed in the fire(做主語).
b. 若關系代詞在從句中做定語,表示物的所有關系時，選用 whose 或of which.
Eg:The children saw an elephant whose legs were hurt badly.
綜上所述，當先行詞為人和物時，若在從句中做主語或是賓語，這時可用選用關系代詞that，做定語時用whose.
II. 關系副詞主要有：where,when 和why.
A. 當先行詞為表示地點的名詞時，定語從句由副詞where引導.
In the sixth century BC, ancient Greece was a country where there were a lot of new ideas.
B. 當先行詞為表示時間的名詞時，定語從句由副詞when引導.
Plato lived at a time when philosophy was very fashionable.
C. 當先行詞為表示原因的名詞時，定語從句由副詞why引導.
Can you tell me the reason why you lied to me?
需要注意的是，限制性定語從句不能被省略，否則句意就不完整，例如I met someone who said he knows you.
通過上面的講解，同學們在雅思寫作過程中對限定性定語從句是否又多了一份了解呢?希望可以有助于您更好的解析英文中的定語從句，從而更好的提高雅思作文中的長難句學習。