Relative Clauses: Defining vs Non-Defining with Examples
Relative clauses, also called adjective clauses, give more information about a noun in a sentence. They begin with relative pronouns like who, whom, which, that, or whose. Understanding the two types — defining and non-defining — is essential for correct punctuation and meaning.
Relative Pronouns
Each relative pronoun has a specific use:
Who is used for people as subjects: The woman who lives next door is a doctor.
Whom is used for people as objects: The man whom I met was kind. (formal; often replaced by who in everyday English)
Which is used for animals and things: The book, which I borrowed, is excellent.
That is used for people, animals, and things in defining clauses: The dog that barked is mine.
Whose indicates possession: The student whose phone rang apologized.
Where refers to places: The restaurant where we ate was great.
When refers to times: The day when we met was rainy.
Why refers to reasons: The reason why I called is urgent.
Defining Relative Clauses
Defining relative clauses (also called restrictive clauses) give essential information about the noun. Without this information, the sentence would not make complete sense. Do not use commas with defining relative clauses.
The woman who lives next door is a doctor. (Which woman? The one who lives next door.)
The book that I borrowed is excellent. (Which book? The one I borrowed.)
Students who study regularly get better grades. (Only those who study — a specific subset)
In defining clauses, that can replace who or which in everyday English: The book that I borrowed or The book which I borrowed are both correct, though that is more common in defining clauses.
Non-Defining Relative Clauses
Non-defining relative clauses (also called non-restrictive clauses) give extra, non-essential information. The main sentence is still clear without this information. Always use commas to separate non-defining clauses. Never use that — use who or which instead.
My sister, who lives in London, is visiting us. (I have one sister; the extra info is incidental)
The Eiffel Tower, which is in Paris, is beautiful. (We know which tower — the extra info is just additional)
President Lincoln, who abolished slavery, was assassinated in 1865. (We know who Lincoln is — the clause adds extra context)
Notice that with non-defining clauses, the sentence can stand alone without the clause: "My sister is visiting us." is a complete sentence.
Omission of Relative Pronouns
In defining relative clauses, the relative pronoun can be omitted when it is the object of the clause (not the subject).
Subject: The woman who lives next door is kind. (cannot omit who — it's the subject of the clause)
Object: The book (that) I read was good. (can omit that — it's the object of the clause)
Test: if the clause has a subject after the relative pronoun, you can omit the pronoun. The book I read (book is object of read). The woman who lives there (who is the subject of lives — cannot omit).
Prepositions in Relative Clauses
When a relative clause includes a preposition, it can go at the end of the clause (informal) or before the relative pronoun (formal).
The person who I was talking to is my boss. (informal — preposition at end)
The person to whom I was talking is my boss. (formal — preposition before whom)
In informal English, prepositions at the end are standard. In formal writing, placing the preposition before the relative pronoun is preferred. With which, the formal pattern is common: The situation in which we found ourselves was difficult.
Common Relative Clause Mistakes
Using that in non-defining clauses is a common error: My car, that is red, is fast should be My car, which is red, is fast. Another mistake is omitting the comma in non-defining clauses. Also, avoid using both a relative pronoun and a personal pronoun: The woman who she lives there is incorrect — use The woman who lives there.
Write Better Sentences with Relative Clauses
Relative clauses add depth and detail to your writing. Use our free reading time calculator to check your text length and review your use of complex sentence structures.
Frequently Asked Questions
What is the difference between defining and non-defining relative clauses?
Defining clauses give essential information and do not use commas. Non-defining clauses give extra information and are set off with commas.
Can I use that in a non-defining relative clause?
No. Non-defining clauses use who (for people) or which (for things), never that.
When can I omit the relative pronoun?
Omit the relative pronoun in defining clauses when it is the object of the clause. Subject pronouns cannot be omitted.
What is the difference between who and whom?
Who is used as a subject (the one doing the action). Whom is used as an object (the one receiving the action). In everyday English, who is commonly used for both.
Can a relative clause modify the whole sentence?
Yes, a non-defining relative clause with which can refer to the entire preceding clause: "He passed the exam, which surprised everyone."