Which vs That

Learn how to avoid grammar errors with which vs that.

Example errors

Look at the example errors below. Can you fix them?

Incorrect
– The university, that has the largest law faculty in the country, recently won an important prize.
– The United Kingdom which has over 60 million inhabitants is one of the largest in Europe.

What are the grammar rules?

1.  Which and that can both be used as relative pronouns (in relative clauses), but they’re used in different ways. To know which one to use, it’s important to understand that there are two kinds of relative clause in English.

2.  We use defining (or restrictive) relative clauses to give essential information about someone or something. This information is needed to understand what or who is being referred to.

Here are some examples.

– This is the university that receives the most government funding.
– The tutor who won the award is taking our class today.

You can use either which or that in a defining relative clause to refer to things. However, note that some academic style guides recommend the use of that with defining relative clauses to make it clear that the information is needed to understand what or who is being referred to. This approach also helps you separate defining and non-defining relative clauses in your own mind. Don’t use a comma with a defining relative clause.

3.  We use non-defining (or non-restrictive) relative clauses to give additional (non-essential) information about someone or something.

Here are some examples.

– Professor Smith, who is my tutor this semester, is very patient and kind.
– The sun, which is almost 150 million kilometres from Earth, is over 4 billion years old.

You must use which in a non-defining relative clause. You must also use a comma. This separates the relative clause from the rest of the sentence, and makes it clear that it’s a non-defining relative clause.

4.  We also use which to give additional (non-essential) information about an entire clause or idea.

Here’s an example.

– Climate change has been worsening, which has resulted in some action being taken.

5.  Here’s a summary of the rules.

Information needed to understand what or who is being referred to

Thing Person
Try to use that. Use who.
Don't use a comma. Don't use a comma.

Additional (non-essential) information

Thing Person
Use which. Use who.
You must use a comma. You must use a comma.

Corrected errors

Here are the corrected errors from the start of the lesson.

Incorrect Correct
– The university, that has the largest law faculty in the country, recently won an important prize. – The university, which has the largest law faculty in the country, recently won an important prize.
– The United Kingdom which has over 60 million inhabitants is one of the largest in Europe. – The United Kingdom, which has over 60 million inhabitants, is one of the largest in Europe.

Quiz

Try the questions below to test what you’ve learnt about which vs that.

Is the use of which/that in these sentences correct or incorrect?

1.  China which has the world’s largest population has experienced a major economic boom in the past few decades. 

2.  House prices have risen significantly, which makes it difficult for young people to purchase a home. 

3.  I’d prefer to do a course that costs less. 

4.  Climate change, that some people once believed to be a myth, has now been firmly established as fact. 

5.  Properties that are located within 5 kilometres of the city centre experienced the strongest price growth this year. 

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Feedback

Click below for the answers.

“Which” isn’t used correctly in this sentence. Because it’s a non-defining relative clause, commas need to be used around it.

Here’s the correct sentence:

“China, which has the world’s largest population, has experienced a major economic boom in the past few decades.”
“Which” is used correctly in this sentence.
“That” is used correctly in this sentence.

“That” isn’t used correctly in this sentence. Because it’s a non-defining relative clause, we need to use “which”.

Here’s the correct sentence:

“Climate change, which some people once believed to be a myth, has now been firmly established as fact.”
“That” is used correctly in this sentence.