That or which?

Have you ever wondered when should you use that and when you should use which? 

Here is a quick tip to help you know the difference.  It's just a tip, so it's not foolproof.  But it works well most of the time, and you can use it as a starting point to learn more from a grammar book.

So, here's the difference:

• A that-clause is essential to the meaning of the sentence because it restricts the set of possibilities
• A which-clause offers extra information that is not essential to the meaning of the sentence.

Here's a concrete example:

A) My paper on auctions that has eight sections is too long.

B) My paper on negotiation, which has eight sections, is too long.

In sentence A, the that-clause introduces information that is essential to the meaning of the sentence: it tells the reader which specific paper you mean.  So if remove the that-clause from the sentence, its meaning would change: the reader would no longer be sure which paper you mean.

In sentence B, the which-clause introduces information that is useful but not essential. If you lifted the entire which-clause out of the sentence, readers would still know exactly which paper you mean. So, the which-clause is not essential to the meaning of the sentence.  

You can think of the commas around a which-clause as handles by which you can lift out the entire clause and still preserve the meaning of the sentence. Look:   ,.........,  (OK, they roughly look like handles)

So are you ready to test your that/which knowledge?

Complete these sentences with that/which, include commas where they belong, and click for the answer.

1) The paper on growth ... Robert Solow wrote is sitting on my desk. 

2) The annual AEA meetings … are held in January are crucial for job market candidates.