Adjective clauses are usually introduced by the relative pronouns who, which and that.

Study the following example.

The boy was caught. He had stolen the purse.

These two simple sentences can be combined into a complex sentence by using an adjective clause.

The boy who had stolen the purse was caught.

Here the subordinate clause ‘who had stolen the purse’ says something about the noun ‘the boy’. It therefore serves the purpose of an adjective.

More examples are given below.

The man arrived in the morning. He is a painter.

The man who arrived in the morning is a painter. (Here the adjective clause ‘who arrived in the morning’ says something about the noun ‘the man’.)

This is a great opportunity. It should not be lost.

This is a great opportunity which should not be lost. OR This is a great opportunity that should not be lost.

Here the adjective clause ‘which should not be lost’ says something about the noun ‘the opportunity’.

This is an old fort. It was built by Emperor Akbar.

This is an old fort which was built by Emperor Akbar.

This is an old fort that was built by Emperor Akbar.

Here the adjective clause ‘which / that was built by Emperor Akbar’ says something about the noun ‘an old fort’.