英语语法：109 Which Versus That

If you're confused about that versus¹ which, don't feel bad. It's one of the most common topics people ask me about. I used to work as a technical writer, and I'd often edit documents in which people used the wrong word. More than once, I'd put in the right word, only to have clients change a perfectly² fine that to a which and send it back to me. In fact, having a client try to overrule my correction of a which to a that was one of the things that pushed me over the edge and made me start the Grammar Girl podcast.

Here's the deal: some people will argue that the rules are more complex and flexible than this, but I like to make things as simple as possible, so I say that you use that before a restrictive clause and which before everything else.
Restrictive Clause--That
A restrictive clause is just part of a sentence that you can't get rid of because it specifically restricts some other part of the sentence. Here's an example:
Gems³ that sparkle often elicit⁴ forgiveness.
The words that sparkle restrict the kind of gems you're talking about. Without them, the meaning of the sentence would change. Without them, you'd be saying that all gems elicit forgiveness, not just the gems that sparkle. (And note that you don't need commas around the words that sparkle.)
Nonrestrictive Clause--Which
A nonrestrictive clause is something that can be left off without changing the meaning of the sentence. You can think of a nonrestrictive clause as simply additional information. Here's an example:
Diamonds, which are expensive, often elicit forgiveness.
Alas⁵, in Grammar Girl's world, diamonds are always expensive, so leaving out the words which are expensive doesn't change the meaning of the sentence. (Also note that the phrase is surrounded by commas. Nonrestrictive clauses are usually surrounded by, or preceded by, commas.) Here's another example:
There was an earthquake in China, which is bad news.
If you leave off the clause that says which is bad news, it doesn't change the meaning of the rest of the sentence.
A quick and dirty tip (with apologies to Wiccans and Hermione Granger) is to remember that you can throw out the “whiches” and no harm will be done. You use which in nonrestrictive clauses, and if you eliminate a nonrestrictive clause, the meaning of the remaining part of the sentence will be the same as it was before.
Needed--That
On the other hand, if it would change the meaning to throw out the clause, you need a that. Do all cars use hybrid⁶ technology? No. So you would say,
"Cars that have hybrid technology get great gas mileage⁷."
Is every leaf green? No. So you would say,
 
"Leaves that are green contain chlorophyll.
It would change the meaning to throw out the clause in those examples, so you need a that. (Also note that the that clause isn't surrounded by commas. Restrictive clauses usually aren't set off by commas.)

Remembering to use that with restrictive clauses and which with nonrestrictive clauses is the best method, but the quick and dirty tip of using which when you could throw out the clause will also get you to the right answer most of the time.

Video of Your Photos
This week, in honor of it being almost my 100th episode, there's a video on the website made up of Creative Commons photos people posted to the Grammar Girl Flickr group. You can find the video in the transcript⁸ of this show at quickanddirtytips.com. I can only promise that it will be up there for a week, so go check it out now.
Administrative⁹ Stuff

There are also links on the website where you can find a transcript of this episode, my contact information, all the other Quick and Dirty Tips podcasts, and preorder my print book. Not only will you be the first one on your block to get it, but some sites are also offering extra discounts on preorders. Check it out. Preorder now!

That's all. Thanks for listening. 
 
 

1 versus   

prep.以…为对手，对；与…相比之下

参考例句：

• The big match tonight is England versus Spain.今晚的大赛是英格兰对西班牙。
• The most exciting game was Harvard versus Yale.最富紧张刺激的球赛是哈佛队对耶鲁队。

2 perfectly   

adv.完美地，无可非议地，彻底地

参考例句：

• The witnesses were each perfectly certain of what they said.证人们个个对自己所说的话十分肯定。
• Everything that we're doing is all perfectly above board.我们做的每件事情都是光明正大的。

3 gems   

growth； economy； management； and customer satisfaction 增长

参考例句：

• a crown studded with gems 镶有宝石的皇冠
• The apt citations and poetic gems have adorned his speeches. 贴切的引语和珠玑般的诗句为他的演说词增添文采。

4 elicit   

v.引出,抽出,引起

参考例句：

• It was designed to elicit the best thinking within the government. 机构的设置是为了在政府内部集思广益。
• Don't try to elicit business secrets from me. I won't tell you anything. 你休想从我这里套问出我们的商业机密, 我什么都不会告诉你的。

5 alas   

int.唉(表示悲伤、忧愁、恐惧等)

参考例句：

• Alas!The window is broken!哎呀！窗子破了！
• Alas,the truth is less romantic.然而，真理很少带有浪漫色彩。

6 hybrid   

n.(动，植）杂种，混合物

参考例句：

• That is a hybrid perpetual rose.那是一株杂交的四季开花的蔷薇。
• The hybrid was tall,handsome,and intelligent.那混血儿高大、英俊、又聪明。

7 mileage   

n.里程，英里数；好处，利润

参考例句：

• He doesn't think there's any mileage in that type of advertising.他认为做那种广告毫无效益。
• What mileage has your car done?你的汽车跑了多少英里？

8 transcript   

n.抄本，誊本，副本，肄业证书

参考例句：

• A transcript of the tapes was presented as evidence in court.一份录音带的文字本作为证据被呈交法庭。
• They wouldn't let me have a transcript of the interview.他们拒绝给我一份采访的文字整理稿。

9 administrative   

adj.行政的，管理的

参考例句：

• The administrative burden must be lifted from local government.必须解除地方政府的行政负担。
• He regarded all these administrative details as beneath his notice.他认为行政管理上的这些琐事都不值一顾。