That vs Which? [Difference explained]

Mary Cullen
Post by Mary Cullen
Originally published January 24, 2021, updated December 17, 2021
That vs Which? [Difference explained]

One of the trickier grammar rules in the English language is the difference between the words that and which. Both serve a similar purpose of clarifying information in a sentence. Their difference is that one is used to present essential information in the sentence and the other is used to present non-essential information in the sentence. 

  • That introduces essential information in a “restrictive clause.” (This is also called an essential adjective clause.)
    Example: Divisions that generate profit often glean admiration.
  • Which introduces extra information in a “nonrestrictive clause.” (This is also called a non-essential adjective clause.)
    Example: We should all pay attention to David’s new product idea, which is likely to triple sales next year.

Let's dive deeper into this challenging grammar concept, and how you can immediately determine the correct answer for that vs which every time you construct a sentence. 


That
example

Below is the correct usage of that:

Divisions that generate profit often glean admiration.

The words that generate profit restrict the divisions you're talking about. Without this restrictive clause of the specific divisions, the meaning of the sentence would change. Without the clarification, you'd be stating that all divisions glean admiration, not just the profitable divisions.

The clause “that generate profit” is essential to the meaning of the sentence, so the correct word is that. You cannot remove the that clause without changing the meaning of the sentence. 

A comma is never needed with that in a restrictive clause. It’s an inverse punctuation relationship  — you need the information for the sentence to make sense so you do not need the commas. Commas set off extra, unnecessary information.

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Which example

Here's the correct usage of which:

We should all pay attention to David’s new product idea, which is likely to triple sales next year.

The second clause provides extra information, and it is not essential to the first clause. Therefore, which is correct. Even if you remove the which clause from the sentence, the sentence remains clear because “David’s new product idea” is specific enough. You could also separate the which clause, change which to a different noun, and you would create two complete sentences. “It is likely to triple sales next year.”

Here’s another example that puts a which clause in the middle of the sentence, instead of at the end as in the previous example:

Let’s talk about the new marketing plan, which I think is weak in several ways, at the team meeting on Friday morning.

“Which I think is weak in several ways” is additional to understanding the sentence. You don’t need that information to understand the sentence's meaning, so which is correct to introduce the additional information.

In both examples of which, notice that there are commas used to set off the clause. A comma is required with which in a nonrestrictive clause. Similar to that, there is an inverse punctuation relationship — if you don’t need the information, you need the commas.



Let’s look at one more example of each.

That:

According to their website, DuPont is a company that uses science and innovation to make the world a safer, healthier, and better place to live. 

You need the information after that in order for this sentence to have clear real meaning, so you don’t need any commas.

Which, with the clause at the end of the sentence:

Let’s discuss the transition plan, which must be clear and effective. 

Here, “the transition plan” is specific enough to carry a full understanding of the sentence. The which clause adds extra information. Since you don’t need the extra info, you do need the comma.

Which, with the clause in the middle of the sentence:

The old schoolhouse, which was one of my favorite historical sites to visit, was restored to become our new office.  

Again, the sentence carries clear meaning without the which clause information. Therefore, the clause uses which, since that information is not essential. Notice how the clause is set off by commas because which is used. Remember, you don’t need the additional information, so you need the commas.

How to remember that vs. which use

Here's a good rule of thumb:

  1. Use: If the meaning of a sentence is altered by removing the words following that or which, use that because the words are essential. If you can remove the words without altering the meaning, use which because the additional words are not essential.

  2. Punctuation: That does not need a comma. Which needs a comma.

Summary

That which doesn’t confuse us makes us better writers!

  • That = no comma = the following information is essential.
  • Which = comma needed = the following information is not essential.

Our online, self-paced Proofreading and Grammar course will help ensure your finished documents are error-free every time.

 

Mary Cullen
Post by Mary Cullen
Originally published January 24, 2021, updated December 17, 2021
Mary founded Instructional Solutions in 1998, and is an internationally recognized business writing trainer and executive writing coach with two decades of experience helping thousands of individuals and businesses master the strategic skill of business writing. She excels at designing customized business writing training programs to maximize productivity, advance business objectives, and convey complex information. She holds a B.A. in English from the University of Rhode Island, an M.A. in English Literature from Boston College, and a C.A.G.S. in Composition and Rhetoric from the University of New Hampshire.

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