一个让无数学习者头疼的问题 (A Question That Troubles Countless Learners)

如果你曾经在写作中犹豫过该用"that"还是"which"，你并不孤单。即使是英语母语者，也经常在这两个词之间犯错。但好消息是，核心规则其实非常简单：取决于你要不要加逗号。

If you have ever hesitated between using "that" or "which" in your writing, you are not alone. Even native English speakers frequently make mistakes with these two words. But the good news is that the core rule is actually very simple: it depends on whether you need a comma.

限制性与非限制性：本质区别 (Restrictive vs. Non-Restrictive: The Essential Difference)

理解"that"和"which"的关键在于理解两种定语从句的区别。限制性定语从句（Restrictive Clause）提供的是必不可少的信息，用来确定所指的对象。如果去掉这个从句，句子的意思就会改变或变得不清楚。

The key to understanding "that" and "which" lies in the difference between two types of relative clauses. A restrictive clause provides essential information that identifies what is being referred to. If you remove this clause, the meaning of the sentence changes or becomes unclear.

例如："The book that I borrowed from the library is overdue." 这里"that I borrowed from the library"是限制性从句，因为如果不加这个信息，我们就不知道是哪本书逾期了。

For example: "The book that I borrowed from the library is overdue." Here, "that I borrowed from the library" is a restrictive clause because without this information, we would not know which book is overdue.

非限制性定语从句（Non-Restrictive Clause）则提供的是补充信息——即使去掉，句子的核心意思仍然完整。这种从句必须用逗号隔开，并且只能用"which"，不能用"that"。

A non-restrictive clause, on the other hand, provides supplementary information—even if removed, the core meaning of the sentence remains intact. This type of clause must be set off by commas and can only use "which," never "that."

例如："The book, which I borrowed from the library, is overdue." 这里，我们已经知道是哪本书了，"which I borrowed from the library"只是额外补充说明这本书的来历。

For example: "The book, which I borrowed from the library, is overdue." Here, we already know which book is being discussed; "which I borrowed from the library" merely adds supplementary information about its origin.

一个简单的判断方法 (A Simple Test)

如果你不确定该用哪个词，试试这个方法：把从句删掉，看句子意思是否改变。如果意思变了，用"that"（不加逗号）。如果意思没变，用"which"（加逗号）。

If you are unsure which word to use, try this method: delete the clause and see if the meaning changes. If the meaning changes, use "that" (without commas). If the meaning stays the same, use "which" (with commas).

再看两个例子：

Consider two more examples:

✅ "Cars that run on electricity are becoming more popular."（限制性：不是所有车，而是电动的那些。）

✅ "Cars that run on electricity are becoming more popular." (Restrictive: not all cars, but specifically electric ones.)

✅ "Tesla's Model 3, which was released in 2017, is still a bestseller."（非限制性：我们已经知道是Model 3，"which"从句只是补充发布时间。）

✅ "Tesla's Model 3, which was released in 2017, is still a bestseller." (Non-restrictive: we already know it is the Model 3; the "which" clause merely adds the release date.)

英式英语的例外 (The British English Exception)

值得注意的是，英式英语在这方面比美式英语更灵活。在英式英语中，"which"经常被用于限制性从句，即使没有逗号。例如，"the car which broke down"在英式英语中完全可以接受。

It is worth noting that British English is more flexible in this regard than American English. In British English, "which" is frequently used in restrictive clauses, even without commas. For example, "the car which broke down" is perfectly acceptable in British English.

但在正式写作和考试中（尤其是雅思、托福），美式英语的规则更被认可：限制性用"that"，非限制性用"which"。遵循这个规则，你在任何正式场合都不会出错。

However, in formal writing and exams (especially IELTS and TOEFL), American English conventions are more widely recognized: use "that" for restrictive clauses and "which" for non-restrictive clauses. Following this rule ensures you will not make mistakes in any formal context.

常见错误与纠正 (Common Mistakes and Corrections)

错误1： 用"which"替代限制性从句中的"that"。

Mistake 1: Using "which" instead of "that" in restrictive clauses.

❌ "The restaurant which we went to was amazing."

✅ "The restaurant that we went to was amazing."

错误2： 在非限制性从句中用"that"。

Mistake 2: Using "that" in non-restrictive clauses.

❌ "My phone, that I bought last week, is already broken."

✅ "My phone, which I bought last week, is already broken."

错误3： 忘记在非限制性从句前后加逗号。

Mistake 3: Forgetting to add commas around non-restrictive clauses.

❌ "Paris which is the capital of France attracts millions of tourists."

✅ "Paris, which is the capital of France, attracts millions of tourists."

实战练习 (Practice Exercise)

判断下列句子应该用"that"还是"which"，并加上必要的逗号：

Determine whether the following sentences should use "that" or "which," and add commas where necessary:

1. The movie _____ I watched last night was incredible.

2. The Eiffel Tower _____ was built in 1889 remains an iconic landmark.

3. Emails _____ contain suspicious links should be deleted immediately.

4. My neighbor's dog _____ is a golden retriever loves to play fetch.

答案： 1. that（限制性，不知道是哪部电影） 2. , which,（非限制性，已经知道是埃菲尔铁塔） 3. that（限制性，特指含有可疑链接的邮件） 4. , which,（非限制性，补充说明狗的品种）

Answers: 1. that (restrictive, identifies which movie) 2. , which, (non-restrictive, adds info about the Eiffel Tower) 3. that (restrictive, specifies which emails) 4. , which, (non-restrictive, adds the breed as extra info)

【重点词汇】

• restrictive clause /rɪˈstrɪktɪv klɔːz/ n. 限制性定语从句 — A clause that provides essential information to identify the noun. 例句：A restrictive clause cannot be removed without changing the sentence's meaning.
• non-restrictive clause /nɒn rɪˈstrɪktɪv klɔːz/ n. 非限制性定语从句 — A clause that adds extra, non-essential information. 例句：Non-restrictive clauses are always set off by commas.
• relative pronoun /ˈrɛlətɪv ˈproʊnaʊn/ n. 关系代词 — A pronoun that introduces a relative clause (who, which, that, etc.). 例句："That" and "which" are both relative pronouns, but they serve different grammatical functions.
• supplementary /ˌsʌplɪˈmɛntəri/ adj. 补充的 — Additional, extra. 例句：Non-restrictive clauses provide supplementary information about the noun.
• convention /kənˈvɛnʃən/ n. 惯例，规范 — A widely accepted practice or standard. 例句：American English conventions for "that" and "which" are preferred in formal writing.
• iconic /aɪˈkɒnɪk/ adj. 标志性的 — Widely recognized and well-established. 例句：The Eiffel Tower remains an iconic landmark of Paris.
• precede /prɪˈsiːd/ v. 在……之前 — To come before something. 例句：A comma should precede a non-restrictive "which" clause.
• clause /klɔːz/ n. 从句 — A group of words containing a subject and a verb. 例句：Understanding clause types is fundamental to mastering English grammar.

【语法要点】

• 限制性 vs. 非限制性定语从句：限制性从句是句子意思的必要组成部分，不加逗号，用"that"；非限制性从句是补充信息，必须加逗号，只用"which"。判断方法：删掉从句，看句意是否改变。
• 逗号的语法功能：在非限制性从句中，逗号不仅仅是标点符号，它传达了"这是额外信息"的语义信号。漏掉逗号会让读者误以为这是限制性从句，从而产生歧义。
• 英美差异意识：英式英语在"that/which"的使用上更宽松，但在国际考试和正式写作中，美式规则是更安全的选择。了解这种差异有助于阅读不同风格的英文材料。