An adjective clause is a subordinate clause which does the work of an adjective. It qualifies a noun or pronoun in the main clause.

An adjective clause is introduced by a relative pronoun (e.g. who, which, whom, that) or a relative adverb (e.g. where, why, how etc.)

• Uneasy lies the head that wears the crown.
• He is the man whom we all respect.
• The reason why I refused the offer is obvious.
• I know the place where he works.

The relative pronoun or relative adverb introducing an adjective clause is sometimes understood and not expressed.

• Eat all (that) you can. (Here the relative pronoun that can be left out because it is understood.)
• I saw a man (whom) I knew. (Here the relative pronoun whom is understood and hence can be left out.)
• The reason (why) I have come here is to meet you.

A to-infinitive is often used as the equivalent of an adjective clause.

• We need a house where we can live in.
• We need a house to live in.
• Give me some water that I may drink.
• Give me some water to drink.
• I have work which I must do.
• I have work to do.
• He has no shoes which he can wear.
• He has no shoes to wear.

Related posts:

1. Adjective clauses
2. Clauses
3. Noun clause
4. What are Phrases and Clauses?
5. Relative Pronouns
6. What are Relative Pronouns and What Do They Do?
7. Forms of the Relative Pronouns
8. Uses of a noun clause
9. How to construct a sentence having a noun clause