In this lesson, I will explain the difference between essential and non-essential relative clauses in a way that is easy to understand. This will help make your writing clearer and more accurate.

What is a relative clause?

A relative clause is a clause that gives more information about a noun. It will begin with a relative pronoun, which is why it is known by that name. Relative clauses cannot function as complete sentences but they are useful for giving extra information.

Here is an example of a relative clause:

I bought the computer that I told you about.

Here, the relative clause “that I told you about” gives us more information about the noun, “computer.” This is an essential relative clause because the first part of the sentence does not make any sense without it. (We’ll discuss that more later.)

Important things to know about relative clauses:

  • They come after the noun (which is known as an “antecedent”)
  • A relative pronoun such as “that,” “which,” or “who” will come at the start
  • They cannot function as a full sentence
  • They may be essential or non-essential

What is an essential relative clause?

An essential relative clause is one that is essential for understanding the clause before it. In other words, the previous clause (and specifically the noun) does not have a definite meaning without the relative clause.

Let’s go back to our previous example:

I bought the computer that I told you about.

This is an essential relative clause because without it the previous part (“I bought the computer”) has no real meaning.

why we use relative clauses

Imagine your friend said to you, “I bought the computer.” Without further context, this would be confusing. You would ask, “What computer?”

As such, people tend to add essential relative clauses to give more information. For example:

  • I bought the computer that you recommended.
  • I bought the computer that your brother told me about.

By adding more information, “the computer” now makes sense. The listener could reasonably guess what computer the speaker is talking about.

Note: If you are struggling to understand this, you might have trouble with articles. A person might also say “I bought a computer.” This makes perfect sense because it refers to a single unknown computer. You can learn about articles here.

How do we use essential relative clauses?

In the above example, I used the relative pronoun “that” to link my clauses but we could use other relative pronouns like “where” or “when” or “who.” We do not use “which” with essential relative clauses.

The important thing is that you should not put them after a comma. This is very, very important.

Here’s an example:

This is the park where I learned to ride a bicycle.

Here, the relative pronoun “where” begins the relative clause. It comes after the noun “park,” which is given more context by the relative clause.

Note that “This is the park” has absolutely no meaning in English. Even if a person points to a park and says it, you would be confused. You would ask something like, “So? What about this park?”

When a sentence has no meaning like that, we should add our relative clause. Make sure that you don’t put a comma before it, though. That would be wrong. We use commas before non-essential relative clauses.

What is a non-essential relative clause?

A non-essential relative clause is similar to an essential one but it adds information that is purely additional. In other words, it is not necessary in order to understand the previous clause. For example:

I sold my computer, which I used to use for work.

The first clause, “I sold my computer,” is a perfectly complete thought. If you said this to someone, they would easily understand you. Because you have said “my,” it has an obvious meaning. Therefore, whatever information you add after it is non-essential.

Here’s another example:

Next year, I’m going to study in Japan, which is my favourite country.

The main clause (“I’m going to study in Japan”) is another perfectly complete idea. If someone said this to you, you would easily understand it. Therefore, to add any additional information, we would use a non-essential relative clause.

How do we use non-essential relative clauses?

A non-essential relative clause also comes after the noun it describes but there should be a comma separating the two parts:

This is Central Park, where I learned to ride a bicycle.

Notice how similar this is to the above example. The difference is that the park now has a proper name. Because of that, it is a definite thing and the first part of the sentence is a complete thought. As such, anything that comes after it is non-essential.

With non-essential clauses, we use a comma and then a relative pronoun like “which,” “where,” or “who.” We do not use “that” with essential relative clauses.

Which vs That

Perhaps the most common relative pronouns for beginning relative clauses are “which” and “that.” These are used a bit more frequently than “who,” “when,” “where,” and so on.

The easiest way to understand their use is this:

  • “That” is used to start an essential relative clause
  • “Which” is used to start a non-essential relative clause

We use “which” after a comma and “that” without a comma.

For example:

  • This is the house that I grew up in.
  • This is my childhood home, where I lived until I was sixteen.

I have a whole article dedicated to “which vs that” here.

More Examples

Here are some more examples of relative clauses. I will put the type (essential/non-essential) after the sentence.

  • This is my friend Jim, whom I met when I was ten years old. (non-essential)
  • He’s the man that I warned you about. (essential)
  • My camera, which I bought just two months ago, is now broken. (non-essential)
  • The shop that just opened near my house has already gone out of business. (essential)
  • I love cooking vegetarian dishes, which are usually healthier than ones with meat. (non-essential)
  • Can I borrow the book that we talked about yesterday? (essential)

A Final Note

The rules for essential and non-essential relative clauses are very simple, as we have seen. However, it is easy to be confused in some situations. The best way to solve this is to think about the main clause. Does it make sense by itself? If it does, then the information that you add will probably be non-essential. If it is necessary to understand the first clause, then it is probably essential.

You also need to remember that a relative clause is part of the same sentence as the first clause. If you write it as a sentence by itself, it will be a sentence fragment because it is incomplete. This would be a major grammatical error.