Understanding relative clauses is essential for mastering complex sentence structures in English. These clauses not only add detail and depth but also help connect ideas clearly and precisely. In this article, we will explore defining and non-defining relative clauses—what they are, how they function, and how to use them effectively in both spoken and written English.
What Is a Relative Clause?
A relative clause is a type of subordinate clause that modifies a noun or a noun phrase. It begins with a relative pronoun (such as who, whom, whose, which, that) or, in some cases, a relative adverb (when, where, why). The clause provides additional information about the noun it modifies.
Relative clauses are broadly divided into two categories:
- Defining relative clauses (also called restrictive clauses)
- Non-defining relative clauses (also called non-restrictive clauses)
Defining Relative Clauses
What Are They?
A defining relative clause gives essential information about the noun it modifies. Without this clause, the meaning of the sentence would change or become incomplete.
Example:
- The woman who lives next door is a doctor.
Here, the clause “who lives next door” identifies which woman we’re talking about. Without it, the sentence “The woman is a doctor” would be too vague.
Common Relative Pronouns in Defining Clauses
| Relative Pronoun | Used For | Example |
| who | people | The man who called you is my uncle. |
| whom | people (formal) | The student whom the teacher praised was happy. |
| whose | possession | The girl whose phone rang was embarrassed. |
| which | things/animals | The car which broke down was expensive. |
| that | people/things (informal) | The book that I borrowed is amazing. |
Note: In informal English, “that” is often used instead of “who” or “which” in defining clauses.
Important Characteristics
- No commas are used.
- Provides crucial information.
- Can use “that” instead of “who” or “which.”
Omitting the Relative Pronoun
Sometimes the relative pronoun can be omitted if it functions as the object of the clause.
Example:
- The movie (that) we watched was thrilling.
Here, “that” can be left out: “The movie we watched was thrilling.”
Non-Defining Relative Clauses
What Are They?
A non-defining relative clause adds extra information about a noun that is already clearly identified. This clause can be removed without changing the fundamental meaning of the sentence.
Example:
- My sister, who lives in Paris, is visiting next week.
Here, “who lives in Paris” is additional information. We already know who the speaker’s sister is.
Common Relative Pronouns in Non-Defining Clauses
| Relative Pronoun | Used For | Example |
| who | people | My uncle, who is 70 years old, still jogs. |
| whom | people (formal) | Sarah, whom you met yesterday, is my friend. |
| whose | possession | Mr. Smith, whose daughter studies with me, is a lawyer. |
| which | things/animals | The house, which was built in 1920, needs repairs. |
Note: “That” is not used in non-defining clauses.
Important Characteristics
- Always separated by commas.
- Adds non-essential information.
- Cannot omit the relative pronoun.
- Cannot use “that” as a substitute for “who” or “which.”
Defining vs Non-Defining: A Quick Comparison
| Feature | Defining Clause | Non-Defining Clause |
| Purpose | Identifies the noun | Adds extra information |
| Use of commas | No | Yes |
| Use of “that” | Yes | No |
| Omission of pronoun | Sometimes possible | Not possible |
| Sentence meaning without the clause | Incomplete or unclear | Still complete and clear |
Relative Adverbs in Both Clause Types
Relative adverbs like when, where, and why can also introduce relative clauses.
- Defining:
This is the house where I was born.
(We need the clause to identify which house.) - Non-Defining:
2001, when I moved to Canada, was a turning point in my life.
(When I moved to Canada is extra information.)
Common Mistakes to Avoid
- Using “that” in non-defining clauses:
Incorrect: My car, that is red, is fast.
Correct: My car, which is red, is fast. - Omitting commas in non-defining clauses:
Incorrect: My brother who lives in London is a chef.
Correct: My brother, who lives in London, is a chef.
(If you have more than one brother, the first version might be correct as a defining clause.) - Using a relative clause without a clear antecedent:
Incorrect: She gave me a book, which was interesting, and left.
(Was the book interesting, or was the act of giving interesting?)
How to Practice Using Relative Clauses
Step 1: Identify the Noun
Before adding a relative clause, clearly identify the noun you want to describe.
Step 2: Decide if the Information Is Essential
Ask yourself whether the additional information is necessary for understanding. If it is, use a defining clause. If not, use a non-defining clause.
Step 3: Choose the Right Relative Pronoun
Use “who” for people, “which” for things, and “whose” for possession. Use “that” only in defining clauses.
Conclusion
Relative clauses are powerful tools in English grammar. By distinguishing between defining and non-defining relative clauses, you can craft sentences that are both precise and elegant. Whether you are writing essays, reports, or simply speaking clearly, mastering these clauses will elevate your English communication skills.