Relative clauses are the "expanding" tools of the English language. They allow you to add essential or extra information about a noun without starting a brand-new sentence. Think of them as the descriptive adjectives of the clause world.
1. The Building Blocks: Relative Pronouns
To start a relative clause, you need a connector. The choice depends on what (or who) you are talking about:
| Pronoun | Used for... | Example |
|---|
| Who | People (Subject) | The chef who won the award is here. |
| Whom | People (Object) | The candidate whom we hired is brilliant. |
| Which | Things/Animals | The book which is on the table is mine. |
| That | People/Things | The car that I bought is hybrid. |
| Whose | Possession | The girl whose cat is missing is sad. |
2. Defining vs. Non-Defining Clauses
This is where most people get tripped up. It’s all about whether the information is essential or just a bonus.
Defining (Restrictive) Clauses
These are necessary to identify the specific noun you are talking about. If you remove it, the sentence no longer makes sense or loses its specific meaning.
Rule: No commas used.
Example: "The students who studied hard passed the exam."
Meaning: Only the specific students who studied passed.
Non-Defining (Non-Restrictive) Clauses
These add extra "flavor" or "interesting facts" about a noun that is already clearly identified.
Rule: Always use commas. You cannot use "that" here.
Example: "My brother, who lives in Tokyo, is a designer."
Meaning: You already know who my brother is; the fact that he lives in Tokyo is just extra info.
3. The "That" vs. "Which" Debate
In American English, we tend to be quite strict about this:
Use that for defining clauses (no commas).
Use which for non-defining clauses (always commas).
Pro Tip: If you can remove the clause and the sentence still "works," use which and commas. If the sentence breaks, use that.
4. When can you drop the pronoun?
You can actually delete the relative pronoun (who, which, that) if it is the object of the clause.
Keep it: "The man who called you is outside." (Who is the subject doing the calling—cannot delete).
Drop it: "The movie [that] we watched was boring." (We is the subject, that is the object—you can safely ditch it).