When Do You Use Which And That? | Rules That Fix Errors

“Which” and “that” feel small, but they steer meaning. One picks a specific thing from a group cleanly. The other drops in extra detail, like an aside you can lift out.

When Do You Use Which And That? The Fast Decision

Start with one question: if you remove the clause, do you still know which person or thing you mean? If the answer changes, you’re in defining territory. If the meaning stays steady, it’s an add-on.

when do you use which and that?

Commas are a fast clue. Commas usually signal a nondefining clause, so “which” fits. No comma often points to “that” in American editing.

Sentence Situation	Safer Choice	Punctuation Cue
You need the clause to identify the noun	that	No commas
You’re adding extra detail about a known noun	which	Commas on both sides
The clause comments on a whole idea, not one noun	which	Comma before which
The clause follows “all,” “everything,” or “anything”	that	No commas
The clause follows a superlative (“best,” “only,” “first”)	that	No commas
You use a preposition right before the relative word	which	Often formal wording
You can drop the relative word and the sentence still works	that (or omit)	Only in defining clauses
The clause sits inside dashes or parentheses	which	Already set off as extra
You’re writing for a British audience or a UK house style	which or that	Either may appear

Using Which And That In Relative Clauses

Most “which” and “that” choices show up in relative clauses, the mini-descriptions attached to nouns.

There are two main types. A defining clause narrows the noun, telling the reader which one you mean. A nondefining clause adds extra info about a noun the reader can already identify.

Do The Removal Test

Read the sentence once with the clause, then read it again without the clause. If the noun becomes vague, the clause defines it. If the noun stays clear, the clause is nondefining.

Try it on this pair. “Students that submit early get feedback first.” Without the clause, “students get feedback first” is unclear. Now try: “My laptop, which I bought last year, still runs well.” Without the clause, you still know which laptop you mean.

Let Commas Decide First

Commas don’t just decorate. They tell the reader whether the clause is woven into the noun or set off as a side note. If you need commas, “which” is the normal pick, and “that” usually sounds off.

If you don’t need commas, “that” is a common pick in American editing, since it keeps defining clauses easy to spot.

When To Use “That” In Defining Clauses

Use “that” when the clause is tied to the noun so tightly that the noun changes without it. In these lines, “that” signals “this one, not the others.”

“The email that contains the invoice is in my inbox.”

Patterns That Pair Well With “That”

Certain setups lean hard toward “that,” since they already push you toward narrowing. If you’re stuck, scan the words right before the clause.

• Indefinite words: all, any, each, every, everything, anything, nothing
• Superlatives and limits: best, worst, first, last, only
• Same and exact: the same, the exact, that exact
• Mixed choices: one of the, a kind of, a type of

When You Can Omit “That”

In defining clauses where the relative word acts as an object, you can often drop it. “The movie (that) we watched” still reads fine.

Don’t omit the word when it is the subject of the clause. “The movie that won” needs the relative word. Without it, the clause collapses.

When To Use “Which” In Nondefining Clauses

Use “which” when the clause adds side info and the reader can already identify the noun. Commas mark that the clause is optional, not part of the noun’s core label.

“My sister’s car, which has a cracked windshield, is in the shop.” The car is already identified; the crack is extra detail.

Why Commas Matter With “Which”

Nondefining clauses are like parentheses you can remove without breaking the sentence’s core meaning. The commas tell your reader, “Pause here; this part is extra.”

In American editing, “which” plus commas is the most reliable pattern. The Chicago Manual of Style gives this split in its Q&A on which vs. that.

“Which” Referring To A Whole Idea

Sometimes “which” points back to the whole clause before it, not to one noun.

“I missed the last train, which meant a long walk home.” In that sentence, “which” links to the fact of missing the train.

When House Style Changes The Usual Split

You’ll hear a strict rule that “that” is always defining and “which” is always nondefining. Many editors follow that pattern because it makes sentences easy to scan.

Some respected references also note that defining “which” shows up often in edited prose, and it can be fine when the sentence stays clear. Merriam-Webster explains this range in its usage note on when to use that and which.

If you’re writing for a school assignment, a workplace style sheet, or a publication, follow the choice that matches that house style. Consistency keeps your reader from stumbling.

Cases That Trip Writers Up

Most mistakes come from punctuation or from clauses that don’t sit right next to the noun they describe. Fix those two issues and your “which” and “that” choices get easier.

Prepositions Before The Relative Word

In more formal writing, you may see a preposition right before the relative word: “the proposal in which we outlined costs.” In that pattern, “which” is common. “That” usually doesn’t follow a fronted preposition.

If you dislike the formal sound, you can move the preposition to the end: “the proposal that we outlined costs in.” It’s plain and normal in everyday English.

Nondefining Clauses Don’t Use “That”

If commas set the clause off as extra, “that” is a poor fit. Write “The report, which was late, caused a delay,” not “The report, that was late, caused a delay.”

This is a common teaching point in grammar resources such as Purdue OWL’s page on that vs. which.

Don’t Let The Clause Drift Away

Place the relative clause right after the noun it modifies. If it drifts, the reader may attach it to the wrong noun, and no “which” or “that” choice can rescue the meaning.

Weak: “She handed Mark the book that was torn.” Did Mark tear it, or was the book torn? Clearer: “She handed Mark the torn book.” If you need the clause, tighten it: “She handed Mark the book that had torn pages.”

Editing Pass: Fix Which And That Without Guessing

When you revise, treat this as a quick sequence, not a vibe check. You’re checking meaning, then punctuation, then house style.

Step 1: Name The Noun

Point to the exact noun the clause modifies. If you can’t, the sentence needs repair. A relative clause should attach to a real noun, not to the air.

Step 2: Run The Removal Test

Cut the clause. If the reader can still identify the noun, put commas around the clause and use “which.” If the noun becomes unclear, remove commas and use “that” in American editing.

Step 3: Check For A Whole-Sentence Link

If the clause comments on the entire idea before it, “which” is the safer choice. This is common after a complete clause followed by a comma.

Step 4: Read For Rhythm

Read it out loud. If commas add a natural pause, keep them. If the sentence feels like one unit, drop them.

Before	After	What Changed
Dogs which bark all night annoy neighbors.	Dogs that bark all night annoy neighbors.	Defining clause, no commas.
My phone that I bought last year still works.	My phone, which I bought last year, still works.	Extra detail needs commas.
The app, that crashes often, needs an update.	The app, which crashes often, needs an update.	Nondefining clause takes which.
The snack which has peanuts is off limits.	The snack that has peanuts is off limits.	Clause identifies which snack.
I failed the quiz, that upset me.	I failed the quiz, which upset me.	Which refers to the whole idea.
Books that are on the top shelf, are dusty.	Books that are on the top shelf are dusty.	Defining clause, commas removed.
Her essay which was short earned a high score.	Her essay, which was short, earned a high score.	Nondefining clause set off.
The only seat which was open was in the back.	The only seat that was open was in the back.	“Only” leans toward that.

Practice: Pick Which Or That And Punctuate It

Try these quickly. Decide whether the clause defines the noun or adds extra detail. Then pick “that” or “which” and add commas if needed. After each item, you’ll see one clean version.

Practice Set One

1. Choose the shoes _____ fit your dress code.
2. My neighbor’s dog _____ is a beagle howls at night.
3. We visited the museum _____ opened downtown last spring.
4. I forgot my badge _____ slowed the line at the door.
5. The article _____ you shared cleared up the rule.

Answers: “Choose the shoes that fit your dress code.” “My neighbor’s dog, which is a beagle, howls at night.” “We visited the museum that opened downtown last spring.” “I forgot my badge, which slowed the line at the door.” “The article that you shared cleared up the rule.”

Practice Set Two

1. All the files _____ were labeled “final” were outdated.
2. This is the first class _____ meets in the new room.
3. Her laptop _____ she uses for school has a sticky trackpad.
4. The storm knocked out power _____ caused the router to reset.
5. Grab the mug _____ has the cracked handle.

Answers: “All the files that were labeled ‘final’ were outdated.” “This is the first class that meets in the new room.” “Her laptop, which she uses for school, has a sticky trackpad.” “The storm knocked out power, which caused the router to reset.” “Grab the mug that has the cracked handle.”

Quick Self Check For Which And That

If you came here thinking “when do you use which and that?” you can usually solve it with three moves: spot the noun, remove the clause, then set punctuation.

When you keep that habit in your writing, your sentences read cleaner, and your meaning stays steady. If a teacher or editor prefers a different split, you can adapt in minutes, since you’ll already know which clauses are defining and which are extra.