限定性定語從句對被修飾的先行詞有限定製約作用，使該詞的含義更具體，更明確。
限定性定語從句的用法
在引導限定性定語從句時，that有時相當於in which,at which,for which或on which
（1）Attitudes towards daydreaming are changing in much the same way that(in which) attitudes towards night dreaming have changed. 人們對白日做夢的態度正在改變，這與人們對夜間做夢的看法的變化有非常相似之處。
（2）I like the music for the very reason that(for which) he dislike it. 我出於某種原因喜歡這種音樂，而他恰恰與我相反。
（3）We arrived the day that(on which) they left. 剛好我們到的那天他們走了。
在限定性定語從句中，當關系代詞在從句中擔任動詞賓語時，關係代詞可省略。
（1）The book (that/ which) I am reading is very interesting. 我在讀的`書很有趣。
（2）Is there anything (that) you wanted? 想要什麼東西嗎?
限制性定語從句與非限制性定語從句用法區別：
一、 句法的功能、表現形式不同
定語從句分爲限制性和非限制性兩種。限制性定語從句不可缺少先行詞，去掉它主句意思往往就不明確了，它與主句之間通常不用逗號分開；非限制性定語從句是對先行詞的附加說明，去掉它也不會影響主句的意思。如：
Do you know the professor who is speaking at the meeting? （限制性定語從句）
English is an important subject, which every student should study well. （非限制性定語從句）
二、 先行詞不盡相同
限制性定語從句的先行詞往往是某一個詞，但非限制性定語從句的先行詞可以是一個詞，也可以是句子的一部分，甚至是整個主句，此時非限制性定語從句一般由which或as引導，as引導非限制性定語從句常用在as is said / known / expected / mentioned / reported / announced等結構中。如：
He has passed the college entrance examination, which makes his parents quite happy.
As is known to everybody, the moon travels round the earth once every month.
三、 關係詞的使用情況有所不同
1． that 不可引導非限制性定語從句。如：
Her father gave her a computer for her birthday，which pleased her a lot.
2． why 不用在非限制性定語從句中，需用for which代替。如：
I told them the reason, for which I didn't attend the party last week.
3． 關係代詞替代情況不同
關係代詞 whom 在限制性定語從句中作賓語時可用 who 代替 whom, 但 whom 在非限制性定語從句中作賓語時不可用 who代替。如：
This is the girl whom (who) I have been in love with for six years.
The young man had a new girl friend, whom he wanted to show all his love for.
4． 關係代詞省略情況不同
關係代詞在限制性定語從句中作賓語時可以省略；非限制性定語從句的所有關係代詞均不可省略。如：
She is the new student (whom / who / that) I want to introduce to you.
All the books there, which have beautiful pictures in them, were written by him.
四、 下列情形用非限制性定語從句
1. 當“不定數量詞 (如some, several) ／ 數詞 ＋ of which ／ whom”表示“整體 (which ／ whom)中的一部分”的概念時。如：
We saw many animals in the zoo, some of which are tigers．
There are fifteen new players in our team, two of whom come from Canada.
2. 當先行詞爲專有名詞或被物主代詞和指示代詞修飾時，其後的定語從句通常是非限制性的。如：
My house, which I bought last year, has got a lovely garden.
Qingdao, where I have been three times, is an attractive city to foreigners.
