‘That’ and ‘Which’ are one of the easiest words in grammar, yet I meet so many people who are unclear when to use ‘that’ and ‘which’.
Here are two versions of one sentence, one with ‘that’ and the other with ‘which’.
Which of the two sentences, do you think, is correct?
- The book, which recently made headlines because of its content, has sold 100 000 copies.
- The book that recently made headlines because of its content has sold 100 000 copies.
I’ll first give you the answer to the question above, rather than making you wait till the end of the article. The sentence with ‘that’ is correct. Also note the parenthetical commas in the first sentence.
Now the rule of thumb!
Use ‘that’ to introduce a restrictive clause and ‘which’ to introduce a non-restrictive (parenthetical) clause. Have restricted and non-restricted created more confusion now? Well, it did when I learnt it the first time. But this is one widely used terminology to differentiate ‘that’ from ‘which’.
Here’s an easy explanation. Use ‘which’ when your purpose is just to add extra information to the sentence. That is, the meaning of the sentence is clear even without adding the extra information. Use ‘that’ when the meaning of the sentence is unclear without the clause. That is, if the clause is removed, the meaning of the sentence will change.
In the example above, the first sentence without the clause reads, ”The book has sold 100 000 copies”. This is unclear. Which book? What was the feature because of which it sold so much? Thus, you definitely need the clause to complete the meaning of the sentence. Hence, the second sentence is correct: The book that recently made headlines because of its content has sold 100 000 copies.
Let’s try with one more example now.
- Lecture room 5, which is newly built, is in building 51.
- Lecture room 5 that is newly built is in building 51.
Now in this case, the sentence with ‘which’ is correct. The ”newly built” clause is adding extra information to the sentence and if removed, does not alter the meaning of the sentence—Lecture room 5 is in building 51.
Another difference between ‘that’ and ‘which’ is that ‘which’ is always supported by parenthetical commas.
Now that you know the difference between ‘that’ and ‘which’, you would ask, ”Is this difference worth bothering”?
While most people would use ‘which’ and ‘that’ interchangeably and it does not result in undue confusion, it is worth knowing the difference to make your writing as clear as possible (especially in technical and business writing).
Just a reminder towards the end; do not use ‘that’ or ‘which’ to refer to people. Use ‘who’ instead.
- Incorrect: The boy that played football is injured.
- Correct: The boy who played football is injured.