Adjective clauses are sometimes called relative clauses. They work like this:
Let’s say you want to describe a car. You can use an adjective:
This is a red car.
Or you can use an adjective clause:
This is a car which is red.
Both ways are grammatically correct. However, the first way sounds better because it is more concise.
On the other hand, when you want to use a longer description, you would use an adjective clause:
This is the car that I told you about.
We use adjective clauses to answer the question ‘which one’ and to give extra information:
Example of an adjective clause describing ‘which one’:
This is the guy who I told you about.
Example of an adjective clause adding extra information:
Martin, who lives in Eastford, takes the train to work every day.
You will notice that the adjective clause may appear in the middle of the sentence or near the end. The adjective clause must appear directly after the thing that it describes:
Describing the subject:
People who throw litter everywhere should be ashamed of themselves.
Describing the object:
People prefer pets that are easy to take care of.
Incorrect:
Employees will be punished who break this rule.
Correct:
Employees who break this rule will be punished.