Types of Relative Clauses
A relative clause is a group of words that modifies a noun or pronoun in the main clause. It works like an adjective, describing or identifying the noun it refers to (called the antecedent). Relative clauses begin with a relative pronoun (who, whom, whose, which, that) or sometimes a relative adverb (where, when, why).
The two types of relative clauses differ in one critical way: whether the information they provide is necessary to identify the noun.
Restrictive vs. Non-Restrictive Relative Clauses
Restrictive clauses narrow down which specific person, place, or thing you're talking about. The information is essential to the sentence's meaning, so you can't remove it without changing what the sentence communicates.
- Not set off by commas
- Often introduced by "that" for things and "who" or "whom" for people ("which" also works for things)
- Example: The book that I borrowed from the library is overdue. (Which book? The one I borrowed. Without the clause, the reader doesn't know which book you mean.)
Non-restrictive clauses add bonus information about a noun that's already clearly identified. You could remove the clause and the sentence would still make complete sense.
- Always set off by commas
- Introduced by "which" for things and "who" for people (never "that")
- Example: My sister, who lives in Paris, is visiting next week. (You already know which sister. The clause just gives extra detail.)
A quick test: try removing the clause. If the sentence loses its specific meaning, the clause is restrictive (no commas). If the sentence still works fine, the clause is non-restrictive (use commas).
Relative Pronouns
A relative pronoun does double duty: it introduces the relative clause and connects it back to the antecedent in the main clause. Choosing the right one depends on two things: what the antecedent is (person, thing, or possession) and what role the pronoun plays inside the clause (subject, object, or possessive).
Specific Relative Pronouns and Their Applications
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Who refers to people and acts as the subject of the relative clause. The woman who won the lottery is my neighbor. ("Who" is the subject of "won.")
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Whom refers to people and acts as the object of the verb or a preposition in the relative clause. The candidate whom we interviewed yesterday was impressive. ("Whom" is the object of "interviewed.")
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Whose shows possession and works for both people and things. The dog whose collar is red belongs to my friend.
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Which refers to things or animals and can appear in both restrictive and non-restrictive clauses. The car, which was parked in the driveway, belongs to my parents. (non-restrictive)
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That refers to people, animals, or things but is used in restrictive clauses only. The movie that we watched last night was terrifying.
One thing that trips people up: in informal English, you can sometimes drop the relative pronoun entirely when it functions as the object of the clause. The movie we watched last night works just as well as The movie that we watched last night. You can't drop it when it's the subject, though. The woman won the lottery is my neighbor doesn't work.
Antecedents
The antecedent is the noun or pronoun in the main clause that the relative clause modifies. It determines which relative pronoun you use:
- Person → who, whom, whose
- Thing → which, that
- Animal → which, that, whose
The antecedent also needs to agree in number with the verb inside the relative clause. In The students who are studying will do well, "students" is plural, so the verb "are" matches. In The student who is studying will do well, the singular antecedent calls for "is."
Getting the antecedent right keeps the connection between the main clause and the relative clause clear. If the antecedent is vague or too far from the relative pronoun, the sentence gets confusing fast.