Dictionary Wiki
An adjective clause, sometimes called a relative clause, is a dependent clause that behaves like a one-word adjective: it latches onto a noun or pronoun and fills in more information about it. These clauses let you fold two sentences into one, answer the unspoken question "which one?", and build writing that feels layered rather than choppy. This guide walks through the pronouns that introduce them, the commas that signal their role, and the traps that trip up even experienced writers.
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
The Clause in One Sentence
An adjective clause is a dependent clause acting in the same role as an adjective — describing, pinpointing, or adding detail to a noun or pronoun known as the antecedent. These clauses almost always begin with a relative pronoun (who, whom, whose, which, that) or a relative adverb (where, when, why).
Single adjective: "The quiet guest nodded."
Adjective clause: "The guest who had flown in from Tokyo nodded."
"Quiet" and "who had flown in from Tokyo" both describe the guest. The clause simply fits in more information than any single adjective could carry.
The Pronouns That Open the Door
Relative pronouns open an adjective clause and take on a grammatical job inside that clause — subject, object, or possessor:
| Pronoun | Use | Example |
|---|---|---|
| who | Subject (people) | "The chef who trained in Lyon runs the kitchen." |
| whom | Object (people) | "The candidate whom we hired starts Monday." |
| whose | Possessive (people/things) | "The novelist whose debut sold out is here tonight." |
| which | Subject/object (things) | "The proposal, which we rejected last quarter, is back on the table." |
| that | Subject/object (people/things) | "The laptop that I repaired works fine now." |
What the Pronoun Does Inside the Clause
Relative pronouns are not just connectors. They play a real grammatical role inside the clause they introduce:
Subject: "The neighbor who owns the bakery waved hello." ("Who" is the subject of "owns.")
Direct object: "The novel that I finished last night was haunting." ("That" is the object of "finished.")
Object of preposition: "The mentor to whom I owe my career retired this year." ("Whom" is the object of "to.")
Possessive: "The violinist whose audition stunned the panel got the seat." ("Whose" marks possession.)
When, Where, and Why
Three relative adverbs — where, when, and why — can launch an adjective clause by marking place, time, or reason:
"That is the cafe where we first talked for hours." (place)
"I still think about the afternoon when the storm rolled in." (time)
"No one explained the reason why the meeting ended early." (reason)
Clauses That Narrow Things Down
A restrictive adjective clause does work the sentence cannot do without. It identifies or defines the noun, and dropping it leaves the reader guessing. Restrictive clauses take no commas.
"Drivers who tailgate cause the most rear-end collisions."
(Which drivers? Only the tailgaters. The clause is essential.)
Remove "who tailgate" and the sentence collapses into "Drivers cause the most rear-end collisions" — a sweeping and untrue claim. The clause restricts the statement to the specific subset of drivers the sentence is actually about.
A Few More to Get the Feel
"The cabin that my grandparents built still stands on the lake."
"Customers who leave reviews tend to come back."
"The documentary that aired last night left everyone speechless."
Clauses That Merely Add Color
A nonrestrictive adjective clause supplies extra information about a noun the reader can already identify. Cut the clause and the sentence still makes perfect sense. Nonrestrictive clauses require commas on both sides.
"My grandmother, who lives in Savannah, is flying up for the holidays."
(I have one grandmother; the clause adds a detail rather than identifying her.)
Strip out "who lives in Savannah" and you still have a complete, unambiguous sentence: "My grandmother is flying up for the holidays."
A Note About "That"
"That" never appears in nonrestrictive clauses. Reach for "who" for people or "which" for things instead:
✗ "My bicycle, that has a flat tire, is in the shed."
✓ "My bicycle, which has a flat tire, is in the shed."
Where the Commas Go
| Clause Type | Commas? | Signal |
|---|---|---|
| Restrictive (essential) | None | Meaning breaks if you remove it |
| Nonrestrictive (extra info) | Required on both sides | Meaning stays put if you remove it |
The Drop Test: Mentally delete the adjective clause. If the noun is still clearly identified and the core meaning survives, it is nonrestrictive — wrap it in commas. If the noun suddenly feels vague or the sentence makes a different claim, it is restrictive and should ride without commas.
Picking Between Who and Whom
Use who when the relative pronoun is the subject of its clause. Use whom when it is the object:
Who (subject): "The coach who changed my game retired in May." (Who changed my game? → who = subject)
Whom (object): "The coach whom I respect most retired in May." (I respect whom? → whom = object)
Shortcut: Try swapping "he/she" or "him/her" into the clause. If "he" or "she" fits the slot, write "who." If "him" or "her" fits, write "whom." ("He changed my game" → who. "I respect him" → whom.)
Picking Between That and Which
American English draws a clean line between "that" and "which":
- "That" belongs with restrictive clauses. No commas.
- "Which" belongs with nonrestrictive clauses. Commas required.
"The bike that has the broken spoke is mine." (Restrictive — tells you which bike.)
"My bike, which has a broken spoke, needs fixing." (Nonrestrictive — adds detail about an already-identified bike.)
British English is looser and often uses "which" in both settings, but sticking with the American split adds clarity in any dialect.
When You Can Drop the Pronoun Entirely
Inside a restrictive clause, the relative pronoun can vanish if it is functioning as the object — never the subject:
"The podcast (that) I recommended keeps getting better." — Object of "recommended"; safe to drop.
"The stranger (whom) I sat beside on the plane became a friend." — Object of "sat beside"; safe to drop.
"The courier who arrived at noon had the package." — Subject of "arrived"; must stay.
Trimming Clauses Into Phrases
You can often shrink an adjective clause into a participial phrase or an appositive to tighten a sentence:
Full clause: "The researchers who are working on the vaccine present their findings next week."
Reduced: "The researchers working on the vaccine present their findings next week."
Full clause: "Mount Fuji, which is a dormant volcano, draws climbers from around the world."
Reduced: "Mount Fuji, a dormant volcano, draws climbers from around the world."
The trick works cleanly when the relative pronoun is the subject of the clause and is paired with a form of "be," or whenever the clause can collapse into a participial phrase without losing meaning.
Mistakes Writers Keep Making
1. Using "That" Where "Which" Belongs
✗ "Tokyo, that is the capital of Japan, is enormous."
✓ "Tokyo, which is the capital of Japan, is enormous."
2. Forgetting the Commas Around Extra Information
✗ "My sister who lives in Tokyo teaches yoga." (suggests you have several sisters)
✓ "My sister, who lives in Tokyo, teaches yoga." (you have exactly one sister)
3. Letting the Clause Drift From Its Antecedent
✗ "She picked a ring out of the display case that sparkled." (Was the display case sparkling?)
✓ "From the display case, she picked a ring that sparkled."
4. Mixing Up People Pronouns and Thing Pronouns
✗ "The drone who crashed..."
✓ "The drone that/which crashed..."
Try These Yourself
Join each pair of sentences into one 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 hook onto nouns and pump more detail into your sentences. Get the restrictive/nonrestrictive split right (no commas for essential information, commas for the optional kind), pick the relative pronoun that matches the job inside the clause, and keep each clause anchored next to its antecedent.