An adjective clause (sometimes called a relative clause) is a phrase that is used to give more information about a noun. Look at this example:

That is the place where James was born.

This sentence is about a place. It uses the phrase "where I was born" to say which place.

Here are some more examples:

He's the man who lives next door.
This is the house where she lived.
These are the souvenirs which Ben and Claire bought in Turkey.

You can see that in every case a phrase is used to give more information about the place, person or thing we are talking about. That phrase is called an adjective clause and we use it inside a sentence to describe something.

What an adjective clause looks like

When you use an adjective clause, you must have these parts:

1. a noun (the thing you are describing);
2. a joining word (relative pronoun or relative adverb);
3. a clause with:
   1. a subject, and
   2. a verb.

Here are some examples:

Why do we use adjective clauses?

We use adjective clauses to identify people and things. We use a phrase (clause). That phrase shows, with an action, why a thing or person is important.

Compare these two sentences:

1. "This is a book," and
2. "This is the book that my wife gave me for Christmas."

Sentence 1 is pretty boring, but sentence 2 is nice. It gives me a little more information about the book and why it is special. Using an adjective clause helps you communicate something extra.

Sometimes names of things mean nothing. People might not know the name of a place, thing or person. So, how do you talk about these things? You use a relative clause. For example:

1. "That's Matthew!" and
2. "That's the guy who teaches me English."

If you are talking to someone who does not know Matthew, then sentence 1 is not really so helpful. If you said, "That's Matthew," the next question from your friend would be, "Who's he?" If you use sentence 2, then you are identifying Matthew by what he does (not his name).

What about this case? You need to borrow something from your co-worker. The only problem is that you don't know the name of the thing in English. You can see it on her desk. Which sentence is better?

1. "Can you pass me that thing?" or
2. "Can you pass me that thing that is between your phone and your mouse?" 

Sentence 2 is going to be faster and easier. If there many things on your co-worker's desk, sentence 1 is not so helpful.

Joining words

When you join an adjective phrase to a noun, you often need a joining word. In English, we use these joining words:

• who;
• where;
• which;
• whose;
• why;
• when; and
• that.

Remember that when we make adjective clauses, we don't use "what" as a joining word.

The joining word must match the noun you are describing:

There are two important things to notice:

1. In every case (except for "whose"), you can use "that". We use "that" all the time, but especially in casual speaking and writing. If you are not sure which word to choose, say "that" and you will probably be OK. You must be careful with "where" cases. You might need a preposition, like "in".
2. "Whose" is used to mean its/her/his. The example above is "the man whose car was stolen". You cannot say sentences like these:
   - "the man whose his car was stolen," or
   - "the man which his car was stolen".

"Who", "which" and "that"

These joining words are special. They can be the subjects or objects of the verbs in the adjective clause.

To understand this, think about a couple of "where" and "when" examples:

1. the city where Mariko rented an apartment.
2. the day when Sally is going to buy a new car.

In phrase 1, "the city" is not the subject or the object of "rent". The subject of "rent" is "Mariko". The object of "rent" is "an apartment". In fact, "the city" is part of the complement (the "C" in SVOC, i.e. "Mariko rented an apartment in Tokyo"). Phrase 2 is the same. "the day" is not the subject or the object of "buy". "A new car" is the object of the verb "buy", and "Sally" is its subject. Sentences that would include the information from these phrases would be something like this:

1. Mariko rented an apartment in Tokyo.
2. Sally is going to buy a new car on Tuesday. 

See how "in Tokyo" and "on Tuesday" come at the end? In these sentences, we know that Mariko lives in Tokyo and that Sally is planning on buying her car on Tuesday. When we use the adjective clauses, "the city where Mariko rented an apartment" and "the day when Sally buys a new car", we replace "in Tokyo" with "the city where" and "on Tuesday" with "the day when".

Now look at some of the examples from before:

1. the guy who/that teaches me English. 
2. the man who/that lives next door.

"Who" is the subject of the verbs "teach" and "live". It is also the word that joins the phrase to "the guy" and "the man".

This small word "who" makes a big difference. What about if we did not have "who" in these sentences?

1. "The guy teaches me English", and 
2. "The man lives next door"

These are complete, full sentences. They are simple subject-verb-object-complement (SVOC) sentences. You cannot use them inside another sentence any more. Using "who" says to native speakers, "The next verb you hear (in these examples, "teach" and "live") is NOT the main verb of my sentence."

You can use "which" in the same way as "who":

1. "the tree which/that grew for a thousand years" and
2. "the building which/that stands on the corner."

"Who" and "which" can also be objects like this:

1. "the person who/that Jeremy saw," and
2. "the fruit which/that monkeys eat."

Maybe Jeremy saw Jane. Maybe Jeremy saw Hide. We don't know, but we can talk about "the person who Jeremy saw". That person is the object of the past verb of "see". Likewise, "which" is the object of "eat". It could be any fruit. We don't know, or we don't need to say, but we can still talk about it when we say "the fruit which monkeys eat".