限定非限定性定語從句

　　“Nonrestrictive Adjective Clauses非限定性定語從句”

An adjective clause set off from the main clause by commas is said to be nonrestrictive.

我們把用“逗號”和主句分開的定語從句叫做“非限定性定語從句”。

Here's an example:

Old Professor Legree, who dresses like a teenager, is going through his second childhood.

老教授Legree，常常穿得像個年輕人，正在經歷第二個童年。

This who clause is nonrestrictive because the information in the clause doesn't restrict or limit the noun it modifies (Old Professor Legree). The commas signify that the adjective clause provides added, not essential, information.

“非限定性”是説，who引導的從句並不是必須的，只是額外增加的信息。也就是説，這個句子去掉who引導的`從句，並不影響主句的整體意思：

Old Professor Legree is going through his second childhood.

老教授Legree正在經歷第二個童年。

　　“Restrictive Adjective Clauses限制性定語從句”

On the other hand, an adjective clause that is restrictive should not be set off by commas.

然而，限制性定語從句是不能夠用逗號和主句隔開的。

An older person who dresses like a teenager is often an object of ridicule.

年齡不小，穿得還像個年輕人的人，通常是遭人嘲笑的對象。

Here, the adjective clause restricts or limits the meaning of the noun it modifies (An older person). A restrictive adjective clause is not set off by commas.

這裏，定語從句限定了它修飾的名詞，即An older person。主句和從句之間沒有逗號。

如果我們把從句去掉，句子就變成：

An older person is often an object of ridicule.

年齡不小的人通常是遭人嘲笑的對象。

可以看出，句子的意思已經發生了嚴重的改變。“凡是年齡不小的人通常都是遭人嘲笑的對象”和原句的意思相差甚遠。

So let's keep in mind two basic rules:

所以，請務必記住：

Nonrestrictive

An adjective clause that can be omitted from a sentence without affecting the basic meaning of the sentence should be set off by commas.

Restrictive

An adjective clause that cannot be omitted from a sentence without affecting the basic meaning of the sentence should not be set off by commas.

再來一個經典的例子：

1. The house, which is blue, is my house.

2. The house that is blue is my house.

句1的場景：咱們倆在路上聊天，我給你指我家，咱倆都知道説的是哪座房子，只不過我加一句which is blue，多説明一下。如果省略為The house is my house，説話雙方依然知道談的是哪座房子，到底是什麼顏色並不影響我們雙方的認知。

句2的場景：你完全不知道我家長什麼樣兒。我説The house that is blue is my house.你通過這個信息才判斷出了我家是哪一座。如果省略為The house is my house你就完全一頭霧水了！

在使用過程中，which可以用在非限定/限定性定語從句中，而that只能用在限定性定語從句中。

體會一下下面兩句話中，限定性和非限定性表達的差異：

非限定：The physical bonds included the network of military garrisons, which were stationed in every province, and the network of stone-built roads that linked the provinces with Rome.

限定：Moreover, the tensions that arose within the Roman state produced literary and artistic sensibilities of the highest order.

另：之前我們説，which最好不要用來修飾整個句子。嚴格上講確實如此，但語法界也存在一些爭議，例如劍橋大學出版社出版的Advanced Grammar in Use中就提到了非限定性從句which修飾整句的情況：

The book won't be published until next year, which is disappointing.

I have to go to hospital on Monday, which means I won't be able to see you.