An adjective clause is a subordinate clause which serves the same purpose as an adjective. It modifies a noun or pronoun in the main clause.
Adjective clauses are introduced by a relative pronoun or relative adverb.
Examples are given below.
Uneasy lies the head that wears the crown. (Here the adjective clause ‘that wears the crown’ modifies the noun head.)
Winston Churchill was a great statesman who also wrote many books. (Here the adjective clause ‘who also wrote many books’ modifies the noun statesman.)
This is the house where I was born. (Here the adjective clause ‘where I was born’ modifies the noun house.)
The reason why she did it is obvious.
Sometimes a relative pronoun may introduce a coordinate clause.
Study the example given below.
I met James who gave me this book. (= I met James and he gave me this book.)
Here the clause ‘who gave me this book’ does not identify James. It is a co-ordinate clause that can stand on its own.
Now study the example given below.
He is the boy who stole the watch.
Here the adjective clause ‘who stole the watch’ identifies and describes the noun ‘boy’. Therefore, it is an adjective clause.
More examples of ‘who’ and ‘which’ used to introduce coordinate clauses are given below.
I called James who came at once. (= I called James and he came at once.)
The prisoner was taken before the General, who condemned him to death. (= The prisoner was taken before the General and he condemned him to death.)