Which vs That

Whether we are reading, writing, or speaking, we come across the words ‘which’ and ‘that’ all the time. They enable us to explain ourselves clearly and provide additional details simply. However, these two little words can make a big difference.

Even the most seasoned writers sometimes get confused when it comes to choosing between using ‘which’ and ‘that’ in a sentence. Although the difference between the two may seem subtle, thanks to the grammarian Henry Watson Fowler, there is actually a foolproof way to check which word to use:

If you can remove the clause without ruining the sentence, use which. If not, use that.

Although that’s really all you need to know, here is some background information to help you understand this issue more deeply.

Use ‘That’ for a Defining Clause

A defining clause provides information that is essential to understanding a sentence. In these cases, use ‘that.’ For example:

Sophia’s car that has a popped tire is stuck in New York.

From this short sentence, the reader understands that Sophia has multiple cars, and that one of them has a popped tire. If you were to remove the defining clause, “that has a popped tire,” you would still understand that Sophia’s car was stuck in New York, but you would have no way of knowing that she has more than one car.

Use ‘Which’ for a Non-Defining Clause

A non-defining clause provides additional information about the sentence that may be interesting, but is not essential to understanding the sentence. These clauses, often separated from the rest of the sentence by commas, can be completely removed without changing the meaning (as in the sentence you just read!). In these cases, use ‘which.’ For example:

Sophia’s car, which has a popped tire, is stuck in New York.

In this sentence, the clause simply comes to provide more details about the car. One could completely remove the clause without changing the meaning of the sentence at all.



How Which & That Change a Sentence

Here are a few more examples that demonstrate the difference between defining and non-defining clauses, and how you can determine whether you need to use ‘that’ or ‘which'.

Healthy relationships, which are constantly evolving, bring happiness and satisfaction to your life.

Healthy relationships that are constantly evolving bring happiness and satisfaction to your life.

The first example presents a non-defining clause, where the sentence is still logical without this additional information about healthy relationships. The second example presents a defining clause, where the point of the sentence is to show how the constantly evolving nature of relationships makes them healthy.

Here is another example.

American culture, which is based on the values of democracy, makes space for people with different beliefs and lifestyles.

American culture that is based on the values of democracy makes space for people with different beliefs and lifestyles.

The first example claims that American culture is based on democratic values, and therefore it makes space for a wide variety of people. The second example suggests that American society only has space for different types of people when it is based on democratic values. These sentences show how one word and a few commas can dramatically change the meaning of a sentence.

While choosing either ‘which’ or ‘that’ can have a massive effect on the meaning of your sentence, as seen above, sometimes the difference is subtle, and either option makes sense.

For example:

Electric cars, which are better for the environment, have become much more popular in recent years.

Electric cars that are better for the environment have become much more popular in recent years.

While the sentence certainly has a slightly different meaning depending on which word is used, either can be used. The goal of the first sentence is to show how electric cars have increased in popularity, while the clause simply comes to tell the reader a bit more about electric cars. The second sentence links the rise in popularity of electric cars to the fact that they are better for the environment in a much clearer manner. Since both sentences are grammatically correct and logical, the author must be fully aware of the message he or she is trying to send in order to know which option to choose.

Common Errors

Because the difference between the two words can be so subtle, especially in speech and informal contexts, it has become common for people to use ‘which’ for both non-defining and defining clauses. For example:

This is the new movie that I was telling you about.

This is the new movie which I was telling you about.

While both options may appear correct to the untrained ear or eye, the second option is incorrect. Not only is it missing a comma, but the clause “that I was telling you about” is essential to the meaning of the sentence. If one were to remove this part of the sentence, it would be left unfinished.

Similarly, it is incorrect to use ‘that’ for a non-defining clause, as in the following examples:

My new shirt, that I bought yesterday, already has a hole in the sleeve.

Tonight is the Lady Gaga concert, that is at the venue on the beach.

Pro Tips

Next time you find yourself confused about whether you should use the word ‘that’ or ‘which,’ return to the goal of your sentence. Ask yourself, “is the information following this word essential to my sentence?” Once you have answered this question, you will know whether it is a defining or non-defining clause and, therefore, which word to use.

If you have already written a sentence and you are not sure whether or not you used the right word, test yourself by rewriting the sentence without the clause. If the sentence still makes sense, you know that it is a non-defining clause that needs the word ‘which.’ If your sentence no longer makes sense, it is a defining clause that needs the word ‘that.’

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