A relative clause is a subordinate clause which post-modifies nouns. The subordinating conjunctions who, whose, which, where, that, when, why, how are used.

There are two types of relative clause: defining and non-defining.

Defining relative clauses refer to which person or thing is being described. They cannot be removed from the sentence without losing the meaning. Compare:

The place is in central London. (there is a need to define which place)
The place where these key decisions are made is in central London. (it is clear to the reader which place)

In some defining relative clauses the conjunction can be removed with an object pronoun:

The countries the Mongols invaded experienced a rapid decrease in population. (or 'The countries that the Mongols invaded ...' or 'The countries which the Mongols invaded ...')

Non-defining relative clauses refer to 'extra information' about a person or thing. Notice the punctuation: the extra information is separated by commas. These clauses (in bold) can be removed and the sentence is still complete. The conjunction that cannot be used.

Intonation is absent in writing, which can result in misunderstandings for the reader.
The World Bank, which had formed concepts of development policy, strongly promoted these practices.
Prusiner, whose greatest honour was winning the Nobel Prize for his work on genomes, taught at several top-flight universities.

Test Yourself

Decide whether the following sentences are defining or non-defining relative clauses.

Many East African countries, which have been experiencing severe drought in recent years, have agreed to collaborate on a series of transnational water projects.

Defining

Non-defining

Solution:

Incorrect.
Incorrect. The clause can be removed without losing the meaning of the sentence. Notice the commas which indicate the extra information.
Correct.
Correct. The clause can be removed without losing the meaning of the sentence. Notice the commas which indicate the extra information.

Negotiators have extended the deadline until tomorrow in a sign that agreement is likely to be reached.

Defining

Non-defining

Solution:

Correct.
Correct. This is a defining relative clause.
Incorrect.
Incorrect. This is a defining relative clause.

Le Vernier discovered the planet we now call Neptune.

Defining

Non-defining

Solution:

Correct.
Correct. Note that the subordinating conjunction can be left out of the defining relative clause.
Incorrect.
Incorrect. Note that the subordinating conjunction can be left out of the defining relative clause.

The cutting-edge photocopier, which can produce 3,800 prints per hour, costs somewhere in the region of £15,000.

Defining

Non-defining

Solution:

Incorrect.
Incorrect. This is a non-defining relative clause.
Correct.
Correct. This is a non-defining relative clause.

The policy which the government outlined before the election may not be achievable.

Defining

Non-defining

Solution:

Correct.
Correct. This is a defining relative clause.
Incorrect.
Incorrect. This is a defining relative clause.

Relative Clauses