That vs. Which: The Comma Test That Settles It Every Time

Priya Sharma

Priya Sharma writes English learning guides for ESL students. Pune-based language enthusiast.

Visual representation of the voice · not a photographic portrait

Quick answer: Use "that" with no commas when the words are needed to know which thing you mean: "The phone that I bought is broken." Use "which" with commas when the words are just extra: "My phone, which I bought yesterday, is broken." If you can delete the words and still know which thing it is, choose "which."↗ Share on X

Use "that" when the information is needed to know which thing you mean, and use "which" with commas when the information is extra. "The phone that I bought yesterday is broken" tells you *which* phone. "My phone, which I bought yesterday, is broken" gives a bonus detail about the only phone you have. If you can delete the words and the sentence still points to the same thing, use "which" and add commas. If deleting them changes the meaning, use "that" and no commas.

That one test solves most cases. The rest of this article shows you how to apply it fast, where people slip, and how to practice until you stop thinking about it.

What is the 10-second test for "that" or "which"?

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Follow these steps every time you are not sure.

1. Find the extra part. Look for the group of words that describes a noun. Example: *"The bus ___ goes downtown is late."* The describing part is "goes downtown."

2. Cover it with your finger. Read the sentence without it: *"The bus is late."*

3. Ask one question: Do I still know which bus?

4. If no (there are many buses, and you need "goes downtown" to know which one), use that, with no commas: *"The bus that goes downtown is late."*

5. If yes (there is only one bus, and "goes downtown" is just a fun fact), use which, with commas: *"The bus, which goes downtown, is late."*

Grammar books call the first type a *restrictive clause* (it limits or "restricts" the meaning) and the second type a *non-restrictive clause* (it adds information without limiting). You do not need to remember the names. You only need the finger test.

Why do the commas matter so much?

The commas are not decoration. They change the meaning of the sentence.

Compare these two:

• *"My sister that lives in Chicago is a nurse."*
• *"My sister, who lives in Chicago, is a nurse."*

The first sentence suggests you have more than one sister, and you are talking about the one in Chicago. The second sentence says you have one sister, and by the way, she lives in Chicago. (We used "who" here because it is a person. More on that below.)

Here is the same idea with things:

• *"The shoes that hurt my feet are in the closet."* You own several pairs. Only the painful ones are in the closet.
• *"The shoes, which hurt my feet, are in the closet."* You are talking about one pair. They hurt, and they are in the closet.

A simple way to remember it: commas are like a pair of hands that can lift the words out. If you can lift them out without breaking the sentence, the commas belong there, and so does "which."

Quick comparison table

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Is it wrong to use "which" without commas?

Not always. This is where many learners get confused, because they see native speakers break the rule.

In British English, people often write "which" without commas for essential information: *"The book which I borrowed is on the table."* Many British readers find this normal.

In American English, most editors and style guides prefer "that" for essential information and save "which" for the comma version. If you are writing for school, work, or an exam in the United States, follow the American preference. It is the safest choice and nobody will mark it wrong.

So the practical rule is:

• Speaking or casual texting: don't worry too much. People will understand you.
• Writing for work, school, or exams: use "that" with no commas and "which" with commas. It looks careful and clear.

When must you use "which" and never "that"?

There are three situations where "that" does not work.

1. After a comma. You cannot write *"My laptop, that is new, is slow."* Once you put commas, you need "which": *"My laptop, which is new, is slow."*

2. After a preposition. Prepositions are small words like *in, on, of, for, with, to*. You say *"the house in which I grew up,"* not *"the house in that I grew up."* (In normal speech, most people say *"the house I grew up in,"* which is also correct and sounds more natural.)

3. When it refers to a whole idea. *"He forgot my birthday, which made me sad."* Here "which" refers to the whole event, not one noun. "That" cannot do this job.

When is "that" the better choice?

"That" is usually better in these cases:

• After words like "all," "everything," "nothing," "something," "anything," and "only." *"Everything that he said was true."* *"This is the only job that pays well."*
• After superlatives (words like *best, worst, first, last*). *"It's the best movie that I've seen this year."*
• When the information is essential, as explained above.

You can also often drop "that" completely when it is not the subject of the clause:

• *"The coffee that I ordered is cold."* → *"The coffee I ordered is cold."*

Both are correct. The short version sounds more natural in conversation. But you cannot drop it when it is the subject: *"The coffee that tastes burnt is mine"* cannot become *"The coffee tastes burnt is mine."*

What about "who" for people?

For people, use "who" in both cases:

• Essential: *"The man who called you is my boss."* (no commas)
• Extra: *"My boss, who called you, is very kind."* (commas)

Using "that" for people in the essential version is also common and accepted in everyday English: *"The man that called you is my boss."* But "who" sounds more polite and more careful in writing. Never use "which" for people. *"The teacher which helped me"* is a mistake.

For animals, both "who" and "that/which" are used. If the animal has a name or is a pet, many people use "who": *"Our dog, who is ten years old, still loves walks."*

What are the most common mistakes learners make?

Here are five mistakes we see again and again, with the fix.

1. Using "that" after a comma.

❌ *My city, that is very old, has a castle.*

✅ *My city, which is very old, has a castle.*

2. Forgetting the second comma.

❌ *The report, which is due Friday is not finished.*

✅ *The report, which is due Friday, is not finished.*

The extra information needs a comma on both sides when it sits in the middle of the sentence.

3. Adding commas to essential information.

❌ *Students, who study every day, pass the test.*

This now says *all* students study every day and pass. That is probably not what you mean.

✅ *Students who study every day pass the test.*

4. Using "which" for people.

❌ *The doctor which treated me was great.*

✅ *The doctor who treated me was great.*

5. Using "what" instead of "that."

❌ *The phone what I bought is broken.*

✅ *The phone that I bought is broken.*

"What" in this position is heard in some local dialects, but it is not standard English.

How can you practice this in 5 minutes a day?

Knowing the rule is not enough. You need your brain to choose the right word fast, without stopping. Here is a simple routine.

Day 1 to 3: Spot them. Read a short news article or a blog post in English. Underline every "that," "which," and "who" that starts a describing clause. For each one, do the finger test. Was the writer right?

Day 4 to 6: Fix them. Write five sentences about your day using "that" (essential). Then rewrite each one using "which" with commas, and notice how the meaning changes. Example:

• *The bus that I take is always late.* (I take one of several buses.)
• *The 42 bus, which I take every morning, is always late.* (The 42 is already identified by its number, so the rest is extra.)

Day 7: Say them out loud. Read your sentences aloud. In speech, the comma version usually has a small pause before and after the extra part, and your voice drops a little. Listening for that pause will help you place commas when you write.

Repeat this cycle for two or three weeks. Most learners find that the choice starts to feel natural after a short period of steady practice.

Practice: choose "that" or "which"

Try these. Answers are below.

1. The keys ___ I lost were in my jacket.

2. Paris, ___ is the capital of France, is expensive.

3. This is the only shop ___ sells fresh bread.

4. My old laptop, ___ I bought in 2015, still works.

5. The email ___ you sent me went to spam.

6. He passed the exam, ___ surprised everyone.

Answers:

1. that (you need it to know which keys)

2. which (Paris is already clear; the capital part is extra)

3. that (after "only")

4. which (you have one old laptop; the year is extra)

5. that (which email? the one you sent)

6. which (refers to the whole idea of passing the exam)

If you got 5 or 6 right, you already understand the rule. If you missed some, go back to the finger test and redo those sentences slowly.

Your next step

Open the last email or message you wrote in English. Find every "that" and "which." Do the finger test on each one, fix the commas, and save a corrected copy. Then do the same with your next message before you send it. After about ten messages, you will start choosing the right word without stopping to think.

FAQ

Can I use "which" without commas?

In British English it is common for essential information. In American English, editors prefer "that" without commas and "which" with commas. For school, work, or exams in the US, follow the American preference.

Can I use "that" for people?

Yes, "the man that called" is common in everyday English, but "who" sounds more careful in writing. Never use "which" for people.

Can I leave out "that"?

Yes, when it is not the subject of the clause: "The coffee I ordered is cold" is fine. You cannot drop it when it is the subject, as in "The coffee that tastes burnt is mine."