想要學好英語六級怎麼能不知道定語從句的用法呢?下面就讓小編為大家講解一下吧。
定語從句也稱為關係從句或形容詞性從句，由關係代詞who, whom, whose, which, that或關係副詞as, when, where, why等引導。關係詞除了起引導作用外，還在從句中指代前面的先行詞，並在從句中擔任一定的成分。如：
The car which was stolen has been found.(which指代先行詞car，在從句中作主語)
The house whose windows are broken is empty.(whose是所有格，在從句中作定語)
I shall never forget the day when I entered the university.(when指代先行詞day，在從句中作時間狀語)
1. 限定性定語從句和非限定性定語從句
定語從句就其與先行詞的關係而言，可分為限定性定語從句和非限定性定語從句。限定性定語從句和先行詞之間沒有逗號，表示對先行詞起修飾限制作用;而非限定性定語從句和先行詞之間有逗號分開，是對先行詞進行補充說明，相當於並列句。如：
He is the man who has strong personality. (限定性定語從句)
My mother, who works abroad, is coming next week. (非限定性定語從句)
注：1)非限定性定語從句不能用that引導，一般用which, as或who(指人)。用which或as引導時，既可以修飾主句的部分內容，也可修飾主句的全部內容。如：
He spoke confidently, which impressed me most. (which指代整個主句，在從句中作主語)
2)as引導的非限定性定語從句既可放在主句之前，也可以放在主句之後，但which或who引導的`非限定性定語從句不能放在主句之前。如：
As we all know, the moon is a satellite of the earth.
The large area is covered with thick snow, which affects people’s life greatly.
3) 在限定性定語從句中，關係代詞作賓語時可以省略;但在非限定性定語從句中，關係代詞作賓語時不能省略。如：
The film (which) I saw last night is about a young teacher. (which可以省去)
She introduced me to her husband, whom I hadn’t met before. (whom不能省去)
2. 通常只用關係代詞that，不用which, who或whom的幾種情況
1)當先行詞是all, everything, nothing, something, anything, little, much, none, few等時，如：
All that you want is here.
2) 當先行詞被all, no, some, any, every, a few, a little, much, only, very等修飾時。如：
There is no person that doesn’t make mistakes.
3) 當先行詞被序數詞或形容詞最高階修飾時。如：
This is the best film that I have ever seen.
4) 當出現兩個或兩個以上的先行詞，並同時兼指人或物時。如：
We are talking about the people and countries that we have visited.
5) 當主句是以which或who開頭的特殊疑問句時。如：
Who is the person that is standing over there?
6) 當定語從句為there be句型時，關係代詞只能用that，但經常可以省略。如：
I know the difference (that) there is between you.
7) 當關系代詞在從句中作表語時，常用that。如：
He does not seem to be the man that he was. 他似乎和過去不一樣了。
3. 與其他詞連用引導的定語從句
As引導定語從句時，可指人也可指物，通常與the same, such, so等連用，形式為：the same … as, such … as, as … as, so … as。as在定語從句中可作主語、賓語、表語等。如：
She knew he felt just the same as she did. 她知道他的感覺與她自己的一樣。(as代替事，作賓語)
I lend you such books as will interest you. 我借給你使你感興趣的書。(as代替物，作主語)
注：the same … as和the same … that的用法不同。as引導的定語從句表示其內容與主句所講的事物“相似”，指同類事物;that引導的定語從句表示其內容與主句所講的事物是“同一個”，指同一事物。如：
This is the same pen as I lost yesterday. 這和我昨天丟的筆一樣。(類似的筆)
This is the same pen that I lost yesterday. 這支筆就是我昨天丟的那支。(同一支筆)
4. “介詞 + 關係代詞”引導的定語從句
在“介詞 + which / whom”結構中，介詞的選擇取決於三種情況：
1)定語從句中謂語動詞與表語的搭配。如：
This is the college in which I am studying.
He is the man about whom we are talking.
2) 先行詞與介詞的習慣搭配。如：
The speed at which the machine operates is known on the meter.
3)當定語從句為最高階時只能用of which;否則用其他介詞。如：
I have five dictionaries of which Longman Dictionary is the best.
I have five dictionaries among which Longman Dictionary is published in UK.
注：不可拆分的動詞短語介詞不能提前，如put up with;有的短語可能有不同的介詞搭配，此時需要根據上下文來確定。如：be familiar with / to, compare with / to等。
有時為表意清楚，還可以在關係副詞where / when前加介詞from, to等。如：
China is the birthplace of kites, from where kite flying spread to Japan, Thailand and India.
