That vs. Which
One of our readers, Justin, recently wrote to ask:
When proofreading a peer’s article on the solar system, I realized that she, and I, are unsure of the proper use of “that” and “which” in a sentence. Below is [SIC] two examples of the same sentence, one using “that” and the other “which.”
- “To our knowledge, it is the only body in the solar system which currently sustains life, although several other bodies are under investigation.”
- “To our knowledge, it is the only body in the solar system that currently sustains life, although several other bodies are under investigation.”
Which is the correct sentence, and what is the general rule of thumb?
Justin, I’ll give you the answer now, rather than making you read to the end of the whole article: the second version of that sentence, using that is correct.
When To Use “That” and When To Use “Which”
Before I come on to the “that”/”which” rule, just a reminder that “who” should always be used when referring to people.
- The boy who threw the ball.
- This is the woman who always wears a black shawl.
When referring to objects, though, the rule for using “that” and “which” correctly is simple:
- THAT should be used to introduce a restrictive clause.
- WHICH should be used to introduce a non-restrictive or parenthetical clause.
If that leaves you more confused than when you began this article, read on…
A restrictive clause is one which is essential to the meaning of a sentence – if it’s removed, the meaning of the sentence will change. For example:
- Chairs that don’t have cushions are uncomfortable to sit on.
- Card games that involve betting money should not be played in school.
- To our knowledge, it is the only body in the solar system that currently sustains life…
A non-restrictive clause can be left out without changing the meaning of a sentence. Non-restrictive clauses are either in brackets or have a comma before and after them (or only before them if they come at the end of a sentence):
- Chairs, which are found in many places of work, are often uncomfortable to sit on.
- I sat on an uncomfortable chair, which was in my office.
Why You Need to Use “That” or “Which” Correctly
Changing that to which or vice versa can completely change the meaning of a sentence. Consider the following examples:
- My car that is blue goes very fast.
- My car, which is blue, goes very fast.
The first sentence uses that – suggesting I own more than one car (and even implying my other cars might not be so fast). This is what happens if we leave out the clause and write:
- My car
that is bluegoes very fast. - My car goes very fast.
The sentence’s meaning has changed: the reader does not know which one of my cars goes very fast.
However, the sentence using which simple informs the reader that my car is blue. We can take the clause out without losing any essential information:
- My car,
which is blue,goes very fast. - My car goes very fast.
“That” and “Which” in Common Usage
It is common today for which to be used with both non-restrictive and restrictive clauses, especially in informal contexts:
- Who ate the cake that I bought this morning?
- Who ate the cake which I bought this morning?
The clause “that I bought this morning” is essential to the meaning – I’m not asking about a cake which I bought yesterday, or this afternoon. Therefore, the first example using “that” is the correct one, but many people would not consider the second ungrammatical.
It is, however, incorrect even in informal contexts to use that for a non-restrictive or parenthical clause. For example, these sentences would be considered incorrect:
- This computer, that I have never liked, is very slow.
- The blue desk, that my father gave me.
An easy way to watch out for these is to look for instances where you have a comma followed by the word that. If I’d know this years ago, it would have saved me a lot of frustration with Microsoft Word!
Even though the usage of which has been relaxed to some extent, it is still better to keep your writing as clear as possible by using which for only non-restrictive clauses, and that for restrictive ones.
So, to return to Justin’s example:
- “To our knowledge, it is the only body in the solar system which currently sustains life, although several other bodies are under investigation.”
- “To our knowledge, it is the only body in the solar system that currently sustains life, although several other bodies are under investigation.”
The second sentence, using that is correct, but many people would consider the first sentence permissable too. In a formal context such as a scientific paper, it is better to use that for total clarity.
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Never mind “which” and “that”. The following is incorrect:
“Below is two examples of the same sentence, one using “that” and the other “which.””
It should read “Below are…”
Great stuff Ali.
I learned a thing or two on this post.
Very good explanation. Thank you. Made up for the skull-splitting “Below is two examples…”
“Below is two examples” is a quote from the reader, and not a mistake by Ali, the author of the post. I will insert a SIC there.
Hmm … but aren’t the following uses of “which” (contained in your own explanation) wrong according to these rules?
A restrictive clause is one which is essential to the meaning of a sentence …
The clause “that I bought this morning” is essential to the meaning – I’m not asking about a cake which I bought yesterday, or this afternoon.
I have been following your posts on grammar. I do appreciate the opportunity to brush up on this. The usuage of improper grammar has a tendency to jump out at me, thereby distracting me from the point being made. You might consider a post on know vs known.
If I’d know this years ago,
Thank you for your very helpful blog.
Great explanation on “that vs. which”. But I wondered about this sentence:
“The woman, who none of us ever liked, always wore a black shawl.”
I thought this sentence would use “whom”. Am I wrong on that? I never could get comfortable with using “who / whom” (among other things), because of the local dialect where I grew up.
Whoops … thanks, Marketeer! Shows how easy it is to get these wrong (can you tell that the “that”/”which” distinction is one I’ve struggled with over the years?) Clearly I typed too quickly!
Daniel, if you could edit it to be:
A restrictive clause is one THAT is essential to the meaning of a sentence …
The clause “that I bought this morning” is essential to the meaning – I’m not asking about a cake THAT I bought yesterday, or this afternoon.
… it would spare my blushes.
Cheers!
Ali
Ali,
I have also struggled with it. The way that usually works for me is to first try THAT and if it “sounds right,” I go with it. Otherwise, it’s probably WHICH. Obviously this is far from foolproof. My first wake-up call was from a client catching an inappropriate WHICH, which, as you can imagine, was quite embarrassing!
Restrictive vs. non-restrictive isn’t actually a question of essential context, though it is related. “Restrictive” means to restrict, or limit, a category, thus indicating one item from all the items in a category. “Non-restrictive” means, well, not being restrictive.
A restrictive phrase, starting with “that,” of course, is used when more than one thing is in a category and you need to indicate the one to which you are referring. For example, “Read the book that is on the table.” In this case, the catagory of “book” has more than one item, i.e., more than one book, so you need to restrict, or limit, the category to one book. After all, you wouldn’t want to other person to read the wrong book! You want him to read the book THAT is on the table.
A non-restrictive phrase, starting with “which,” of course, is used when a category only has one item, so you do not need to restrict, or limit, it, though you may wish to provide more information about the thing in question. For example: “Read this book, which is by my favorite author.” Here, “this book” is a categoy of one item, so it does not need restriction. The non-restrictive phrase provides extra information about “this book,” i.e., the author.
As you note, this is a very common problem, so common, in fact, that we added an article about it in our training manual. It will probably come up on our Perfect Writing Forum, which was recently opened.
An error in punctation occurs in the first sentence of the message from Justin; “…I realized that she, and I, are unsure of the proper use…”. The commas are incorrectly inserted after “she” and before “are”. Let us all be correct here.
@Danica,
I’m not a grammar expert. Although, I do some spelling and grammar Nazism sometimes. Daniel knows about it.
Usage of whom is sparse nowadays. You can simple replace whom with who in most of the places.
If this topic has not been covered already, I request blog authors to consider for their future posts.
Thanks to Ali for the great article. Keep them coming.
“The boy who threw the ball.”
Isn’t this a sentence fragment?
Danica, you’re correct. It should be “whom”.
I remember when to use “whom” when someone “does” something to the object of the sentence.
In that sentence, the woman is the object and she suffers from being disliked. So you should use “whom”.
In all other instances you should use “who”. Is that a good explanation?
@Sudheer and Danica: Please do not think this usage is in decline.
@Danica: Interesting point. The who/whom distinction is one I struggle with too
I believe that “whom” WOULD be more grammatical in that sentence, but as others have pointed out, it seems to be used less and less…
I’ll change the example, the last thing I want to do is cause confusion! And perhaps I’ll do some research on the who/whom question for a future article — I think Tarah gives a really good, succinct explanation above.
Thanks for the comments, all of you.
Ali
Thank you, thank you, thank you for this concise, clear explanation.
Who/whom as I was taught is a simple choice. “Who” is used as a subject, whom as an object. Example: “It is she to whom I speak.”
Object of the preposition “to.” “Who is it to whom I speak.” Who with
a predicate nominative. “Who speaks?” Subject of sentence. There are
just not as many instances of whom use. (I don’t mind sentence fragmentation.)
Thank you all for the explanations. I appreciate the way everyone here seems to enjoy language; it’s not something I see very much where I live.
hi,
i was interested in improving my writing skills so i decided to see what the web could offer me and i stumbled on this site. can i tag along and see if i could learn a few things?
thanks.
Since the topic seems to have shifted to “who” vs. “whom”:
I remember OJ’s lawyer (Johnny Cochran?) saying, “Who is kidding whom?” Well said, OJ-lawyer-guy!
Actually, since we have had to address this so many times in our work, we’ll probably add it to our training manual–which is to say, if you’re a bit confused by this, don’t worry. You’re not alone.
This problem, which many people have, is one that is easily corrected with a little understanding and practice.
oke thanks is this make i understanding in usage word ro speak becouse i was learning speaking english
my father owns a car. is the sentence correct?