An adjective clause—also known as a relative clause—is a dependent clause that modifies a noun or pronoun, just as a single adjective would. Adjective clauses allow you to combine sentences, add essential details, and create more sophisticated writing. Understanding how to construct and punctuate adjective clauses is a key skill for any English writer. This comprehensive guide covers relative pronouns, the distinction between restrictive and nonrestrictive clauses, punctuation rules, and common pitfalls.
Table of Contents
- What Is an Adjective Clause?
- Relative Pronouns
- Relative Adverbs
- Restrictive (Defining) Clauses
- Nonrestrictive (Non-defining) Clauses
- Punctuation Rules
- Who vs. Whom in Adjective Clauses
- That vs. Which
- Omitting the Relative Pronoun
- Reducing Adjective Clauses to Phrases
- Common Errors
- Practice Exercises
What Is an Adjective Clause?
An adjective clause is a dependent clause that functions as an adjective—it describes, identifies, or gives more information about a noun or pronoun (called the antecedent). Adjective clauses typically begin with a relative pronoun (who, whom, whose, which, that) or a relative adverb (where, when, why).
Single adjective: "The tall man waved."
Adjective clause: "The man who was standing by the door waved."
Both the adjective "tall" and the clause "who was standing by the door" modify "man." The clause provides more detailed information than a single adjective can.
Relative Pronouns
Relative pronouns introduce adjective clauses and serve a grammatical function within the clause (subject, object, or possessive):
| Pronoun | Use | Example |
|---|---|---|
| who | Subject (people) | "The student who studies hardest will succeed." |
| whom | Object (people) | "The person whom I called didn't answer." |
| whose | Possessive (people/things) | "The artist whose painting won is here." |
| which | Subject/object (things) | "The book, which I read last week, was excellent." |
| that | Subject/object (people/things) | "The car that I bought is blue." |
Functions Within the Clause
The relative pronoun can serve different roles inside the adjective clause:
Subject: "The woman who lives next door is a doctor." ("Who" is the subject of "lives.")
Direct object: "The book that I borrowed was fascinating." ("That" is the object of "borrowed.")
Object of preposition: "The colleague with whom I work is reliable." ("Whom" is the object of "with.")
Possessive: "The student whose essay won received a scholarship." ("Whose" shows possession.)
Relative Adverbs
The relative adverbs where, when, and why can also introduce adjective clauses. They modify the noun by indicating place, time, or reason:
"This is the restaurant where we had dinner." (place)
"I remember the day when we first met." (time)
"The reason why she left is unclear." (reason)
Restrictive (Defining) Clauses
A restrictive adjective clause provides essential information that identifies or defines the noun it modifies. Without the clause, the sentence would lose its specific meaning or become unclear. Restrictive clauses are not set off by commas.
"Students who study regularly perform better on exams."
(Which students? Those who study regularly. The clause is essential for meaning.)
If you remove "who study regularly," the sentence becomes "Students perform better on exams"—a much broader and different claim. The clause restricts (narrows down) which students the sentence is about.
More Restrictive Clause Examples
"The house that Jack built is on this street."
"People who live in glass houses shouldn't throw stones."
"The movie that we watched was terrifying."
Nonrestrictive (Non-defining) Clauses
A nonrestrictive adjective clause provides additional, nonessential information about a noun that is already clearly identified. The clause can be removed without changing the fundamental meaning of the sentence. Nonrestrictive clauses must be set off by commas.
"My sister, who lives in London, is visiting next week."
(I have one sister; the clause adds extra information but doesn't define which sister.)
Removing "who lives in London" still leaves a clear, complete sentence: "My sister is visiting next week."
Important Note on "That"
The relative pronoun "that" is never used in nonrestrictive clauses. Use "who" (for people) or "which" (for things) instead:
✗ "My car, that is red, needs new tires."
✓ "My car, which is red, needs new tires."
Punctuation Rules
| Clause Type | Commas? | Signal |
|---|---|---|
| Restrictive (essential) | No commas | Removing it changes the meaning |
| Nonrestrictive (extra info) | Commas required | Removing it doesn't change the core meaning |
The Comma Test: Read the sentence without the adjective clause. If the sentence still identifies the noun clearly and the meaning is basically the same, the clause is nonrestrictive and needs commas. If the meaning changes or becomes vague, the clause is restrictive and should not have commas.
Who vs. Whom in Adjective Clauses
Use who when the relative pronoun is the subject of the clause. Use whom when it is the object:
Who (subject): "The teacher who inspired me retired last year." (Who inspired me? → who = subject)
Whom (object): "The teacher whom I admire retired last year." (I admire whom? → whom = object)
Quick test: Substitute "he/she" or "him/her" into the clause. If "he/she" works, use "who." If "him/her" works, use "whom." ("He inspired me" → who. "I admire him" → whom.)
That vs. Which
In American English, there is a useful distinction between "that" and "which":
- "That" introduces restrictive (essential) clauses. No commas.
- "Which" introduces nonrestrictive (nonessential) clauses. Use commas.
"The car that has the dent is mine." (Restrictive—identifies which car)
"My car, which has a dent, needs repair." (Nonrestrictive—adds info about an already-identified car)
British English often uses "which" for both restrictive and nonrestrictive clauses, but maintaining the that/which distinction improves clarity in all varieties of English.
Omitting the Relative Pronoun
In restrictive clauses, the relative pronoun can be omitted when it functions as the object of the clause (not the subject):
"The book (that) I read was excellent." — Object of "read"; can be omitted.
"The woman (whom) I met was kind." — Object of "met"; can be omitted.
"The man who called is here." — Subject of "called"; CANNOT be omitted.
Reducing Adjective Clauses to Phrases
Adjective clauses can sometimes be reduced to shorter participial phrases or appositives for more concise writing:
Full clause: "The students who are studying abroad will return in May."
Reduced: "The students studying abroad will return in May."
Full clause: "The Eiffel Tower, which is a famous landmark, attracts millions."
Reduced: "The Eiffel Tower, a famous landmark, attracts millions."
Reduction is possible when the relative pronoun is the subject of the clause and is followed by a form of "be," or when the clause can be converted to a participial phrase.
Common Errors
1. Using "That" in Nonrestrictive Clauses
✗ "Paris, that is the capital of France, is beautiful."
✓ "Paris, which is the capital of France, is beautiful."
2. Missing Commas in Nonrestrictive Clauses
✗ "My brother who lives in Texas is a teacher." (implies multiple brothers)
✓ "My brother, who lives in Texas, is a teacher." (I have one brother)
3. Placing the Clause Too Far from Its Antecedent
✗ "She bought a dress at the store that was on sale." (Was the store on sale?)
✓ "At the store, she bought a dress that was on sale."
4. Using "Who" for Things or "Which" for People
✗ "The car who broke down..."
✓ "The car that/which broke down..."
Practice Exercises
Combine each pair of sentences using an adjective clause:
- "The woman is my neighbor. She drives a red car."
- "I visited a museum. The museum had a Picasso exhibit."
- "The restaurant was excellent. We ate there last night."
- "The boy won the race. His father is my coach."
Answers: 1. "The woman who drives a red car is my neighbor." 2. "I visited a museum that had a Picasso exhibit." 3. "The restaurant where we ate last night was excellent." 4. "The boy whose father is my coach won the race."
Key Takeaway: Adjective clauses add detail and specificity to your writing by modifying nouns with dependent clauses. Master the distinction between restrictive (no commas, essential) and nonrestrictive (commas, extra info) clauses, choose the correct relative pronoun, and place your clauses close to their antecedents for maximum clarity.