Part 1: Imagine every noun in English lives in a big crowded world.
There are many students, many phones, many teachers, many restaurants.
If you just say: “The student is late.”
Your listener thinks: “Which student?”
That’s when English gives you a special tool: an identification code. That code is a defining relative clause.
There are many students, many phones, many teachers, many restaurants.
If you just say: “The student is late.”
Your listener thinks: “Which student?”
That’s when English gives you a special tool: an identification code. That code is a defining relative clause.
Part 2: What does a defining clause really do?
It answers the silent question: “Which one exactly?”
Example: The student who sits next to me is late.
Now the noun has an identity. The clause works like a scanner narrowing the group.
Part 3: Think of it like a filter
Imagine ten students in a classroom.
Sentence without clause: The student forgot their homework. (We don’t know who.)
Now add a filter: The student who was absent yesterday forgot their homework.
The clause removes nine students. Only one remains.
That’s why it’s called defining. It defines the noun.
Now add a filter: The student who was absent yesterday forgot their homework.
The clause removes nine students. Only one remains.
That’s why it’s called defining. It defines the noun.
Part 4: “By the way” clause
Unlike defining relative clauses, a non-defining relative clause gives extra information about someone or something. It isn't essential for understanding who or what we are talking about.
My grandfather, who's 87, goes swimming every day. (We already know which grandfather we mean.)
The house, which was built in 1883, has just been opened to the public. (The clause adds extra information about the house. The sentence is clear even without this detail.)
We always use a relative pronoun or adverb to start a non-defining relative clause: who, which, whose, when, or where (but not "that"). We also use commas to separate the clause from the rest of the sentence.
My grandfather, who's 87, goes swimming every day. (We already know which grandfather we mean.)
The house, which was built in 1883, has just been opened to the public. (The clause adds extra information about the house. The sentence is clear even without this detail.)
We always use a relative pronoun or adverb to start a non-defining relative clause: who, which, whose, when, or where (but not "that"). We also use commas to separate the clause from the rest of the sentence.
Part 5: The Structure Blueprint
A relative clause:
- comes directly after the noun;
- starts with a relative pronoun;
- contains a subject + verb
Formula:
Noun + who/which/that/whose + clause
Example:
The movie that we watched last night was shocking.
Noun + who/which/that/whose + clause
Example:
The movie that we watched last night was shocking.
My teacher, who studied in Oxford, explains grammar very clearly.
Part 6: Choosing the Right “Key”
Think of relative pronouns as keys:
who — opens the “people” door
which — opens the “things” door
that — universal key (people + things, informal)
whose — shows possession
Example:
The girl who won is my cousin.
The laptop that stopped working is mine.
The boy whose jacket was stolen is upset.
Part 7: The Invisible Pronoun Trick
Sometimes the key in defining relative clauses disappears. If the relative pronoun is the object, you can remove it.
The book that I bought is expensive.
The book I bought is expensive.
Why? Because “I” is the subject. The clause still works.
But:
The man who lives here is friendly.
You cannot remove “who.”
Because “who” is the subject of “lives.”
Part 8: When Do We Use Them?
Use defining relative clauses when:
Sometimes the key in defining relative clauses disappears. If the relative pronoun is the object, you can remove it.
The book that I bought is expensive.
The book I bought is expensive.
Why? Because “I” is the subject. The clause still works.
But:
The man who lives here is friendly.
You cannot remove “who.”
Because “who” is the subject of “lives.”
Part 8: When Do We Use Them?
Use defining relative clauses when:
- there is more than one possible noun;
- you must specify;
- the information cannot be removed.
Use non-defining relative clauses when:
- you add extra information about a person or thing that is already clearly identified;
- you talk about something specific or unique, so the listener already knows what you mean;
- you want to add background or descriptive information about people, places, or things.
Final Big Idea
A defining relative clause gives essential information that identifies exactly who or what we mean, while a non-defining relative clause adds extra information that is not necessary for understanding the main idea and is separated by commas.
A defining relative clause gives essential information that identifies exactly who or what we mean, while a non-defining relative clause adds extra information that is not necessary for understanding the main idea and is separated by commas.