What are relative clauses? How are they used (explanation)?

In general, the use of relative clauses introduced by relative pronouns or relative adverbs provides further information. Moreover, English grammar makes a substantial distinction between defining relative clauses (also called restrictive) and non-defining relative clauses (also called non-restrictive). Compare the following usage of both types in detail:

1. On the one hand, defining relative clauses provide information necessary for the understanding of the statement. This type of subordinate clause cannot be omitted, and commas do not separate it from the rest of the sentence:
   • “The girl who is sitting next to Peter is my sister.”
     • Without a relative clause, one would need to ask: “Which girl?”
   • “The car that was stolen was brand new.”
     • Without the relative clause, it would also be necessary here to ask: “Which car?”
   • Attention: If the relative clause were omitted in these cases, the sentence’s meaning would be unclear, or it would result in a different sense.
2. On the other hand, non-defining relative clauses give you additional information that is only supplementary and not essential to the meaning and understanding of the statement. In terms of writing, it is crucial to separate this subordinate clause from the rest by commas:
   • “That shopping centre, which is the largest in the area, opens seven days a week.”
   • “My boss, who is an Italian, is 42 years old.”
   • Attention: By omitting these relative clauses, the meaning would still be the same. They are therefore unnecessary for comprehension.

Note: It is not always easy to tell whether a relative clause is restrictive or non-restrictive. Tip: When pronouncing the complete sentence, pay attention to whether you make a brief pause before the subordinate clause. If this is the case, then it is non-restrictive, which is not necessary. So, commas must be used. If you do not pause and continue speaking fluently, it is restrictive or a necessary clause without commas.

What relative pronouns stand in which relative clauses?

Not every relative pronoun can be used in every relative clause. Additionally, it depends on what the pronoun replaces:

Relative pronoun	Relative clause (restrictive)	Relative clause (non-restrictive)
who	persons	persons
whom (only as object)	–	persons
which	things, animals (only British English)	things, animals
that	persons, things, animals	–

What are the particularities when using relative clauses?

Furthermore, it is still possible to differentiate between both types (restrictive and non-restrictive relative clauses) regarding whether the relative pronoun is the subject or the object in the sentence. If you use it as an object, you can also omit it. The difference is detailed. Compare the following usage carefully:

Relative pronoun as subject

When the relative pronoun takes on the role of the subject (What does the subject do?), the following applies:

• In defining (restrictive) relative clauses, these pronouns are possible:
  • ‘who’ or ‘that’ (for persons/people)
  • ‘that’ and in British English also ‘which’ (for things and animals)
  • Examples:
    • Possibility 1: “Hotel guests who arrive before noon get free lunch.”
    • Possibility 2: “Hotel guests that arrive before noon get free lunch.”
• In non-defining (non-restrictive) relative clauses, only these two pronouns are common:
  • ‘who’ (for persons/people)
  • ‘which’ (for things and animals)
  • Example:
    • “Apple pie, which is one of my favourite cakes, is very easy to make.”

Relative pronoun as object

If the relative pronoun appears functioning as an object (What does the object do?), the following changes:

• The relative pronoun is not required in the defining (restrictive) relative clause and can be omitted. This type is called a contact clause:
  • ‘who’ or ‘that’ (for persons/people)
  • ‘that’ or ‘which’ in British English (for things and animals)
  • Examples:
    • Possibility 1: “The film which we have just watched is exciting.”
    • Possibility 2: “The film that we have just watched is exciting.”
    • Possibility 3: “The film we have just watched is exciting.”
      • Alternatively, it is also possible without the relative pronoun.
• In the non-defining (non-restrictive) relative clause, however, it is mandatory:
  • ‘who’ or ‘whom’ (for persons/people); see also the use of ‘who’ and ‘whom’
  • ‘which’ (for things and animals)
  • Examples:
    • “Have you spoken to Professor Miller again, whom you met the other day?”
    • “My new car, which I bought from my friend, is perfect.”
    • Careful: In unnecessary subordinate clauses, only ‘which’ can represent things. Likewise, the relative pronoun cannot be left out.

Further explanations referring to ‘English relative clauses’

The following explanations are related to the English grammar and syntax topic ‘Defining and non-defining relative clauses’ and also help you learn:

• Using participle clauses
• The present participle (ing form)
• The past participle (3rd verb form)
• Linguistic details on ‘relative clause’
• List of exercises about sentences, clauses, syntax