Adjective Clause

Here are some interactive examples to help explain the difference between single-word adjectives, adjective phrases, adjectival phrases, and adjective clauses. In each adjective clause, the subject is blue, and the verb is green. (Also, in each adjective phrase, the head adjective is shown in bold.)

More Examples of Adjective Clauses

The carpets that you bought last year have rotted.
The follies which a man regrets most in his life are those which he didn't commit when he had the opportunity . (US journalist Helen Rowland, 1876-1950) (Even though this is a quotation by an American journalist, nowadays, most writers in the US would use that instead of which. There's more on this below.)
Bore: a person who talks when you wish him to listen .

The Components of an Adjective Clause

An adjective clause (also called a relative clause) will have the following three traits:

Trait 1. It will start with a relative pronoun (who, whom, whose, that, or which) or a relative adverb (when, where, or why). (This links it to the noun it is modifying.)
(Note: Quite often, the relative pronoun can be omitted. However, with an adjective clause, it is always possible to put one in. There is more on this below.)
Trait 2. It will have a subject and a verb. (These are what make it a clause.)
Trait 3. It will tell us something about the noun. (This is why it is a kind of adjective.)

Look at the three traits in this example: adjective clause example

Quite often, the relative pronoun is the subject of the clause. Look at the three traits in this example: adjective clause traits

The Relative Pronoun Can Be Omitted

It is common for the relative pronoun to be omitted. Look at these examples:

The carpets ~~which~~ you bought last year have gone moldy.
The film ~~which~~ you recommended scared the kids half to death.
The follies ~~which~~ a man regrets most in his life are those ~~which~~ he didn't commit when he had the opportunity . (Helen Rowland, 1876-1950)

This is not always possible though:

Bore: a person ~~who~~ talks when you wish him to listen .

When the adjective clause starts with a relative adverb (when, where or why), the relative adverb cannot be omitted.

I don't remember a time when words were not dangerous . (Libyan author Hisham Matar) (You can often omit a relative pronoun, but you can't omit a relative adverb. So, you can't omit when in this example.)

Why Adjective Clauses Are Important

There are two common questions related to adjective clauses.

(Question 1) Should I use a comma before which?

This is by far the most common question related to adjective clauses. The answer applies to all adjective clauses, not just those that start with which.

Don't use commas if your clause is essential; i.e., it is required to identify its noun. (This is called a restrictive clause.)
Do use commas if your clause is just additional information. (This is called a non-restrictive clause.)

A Good Tip

If you would happily put brackets around it or delete it, then use commas.

Here is an example of a non-restrictive clause: non-restrictive adjective clause example

My brother, who claimed to have a limp , sprinted after the bus. (This clause is not required to identify My brother. It is just additional information.)
My brother (who claimed to have a limp) sprinted after the bus. (As it's just additional information, you can put it in brackets.)
My brother sprinted after the bus. (As it's just additional information, you can even delete it.)

Compare this to a restrictive clause: restrictive adjective clause example

The tramp who claimed to have a limp sprinted after the bus. (This clause is required to identify The tramp. Without it, we don't know which tramp we're talking about.)
The tramp (who claimed to have a limp) sprinted after the bus. (This sentence is only appropriate if we know which tramp we're talking about.)
The tramp sprinted after the bus. (This sentence is only appropriate if we know which tramp we're talking about.)

(Question 2) What's the difference between that and which?

Which and that are interchangeable, provided we're talking about which without a comma.

When which starts a restrictive clause (i.e., a clause not offset with commas), you can replace it with that. In fact, Americans will insist you use that instead of which for a restrictive clause.

Mark's dog which ate the chicken is looking guilty. (but in America or at least widely disliked) (Americans baulk at which without a comma. They insist on that.)
Mark's dog that ate the chicken is looking guilty. (This version is acceptable for all. It will stop you getting hate mail from Americans.)

For many, even Brits, that sounds more natural with a restrictive clause. And, this is something we can use. If all this talk of restrictive and non-restrictive clauses is confusing, try replacing your which with that. If your sentence still sounds good, you almost certainly want which without a comma. This trick works because that can only be used with a restrictive clause, and – whether you consciously know it or not – some language-processing area of your brain does.

The burglar who is suing the homeowner was booed in court.
The burglar that is suing the homeowner was booed in court. (Substituting who for that is a good way to test whether an adjective clause needs commas or not, but some of your readers might not like that being used for a person – even a burglar. So, if your clause starting who sounds okay with that, then revert to who without commas.)

Key Points

If you'd happily delete your clause, then it's not a restrictive clause, and it should be offset with commas.
Don't start a restrictive clause with which if you're American or writing to Americans. Use that instead.
Use who not that for people. Who is a bit sharper.

This page was written by Craig Shrives.