How to Use 'Which' vs 'That' in English: Restrictive and Non-Restrictive Clauses

Let's settle this once and for all. The difference between "which" and "that" isn't some obscure grammar rule for editors only. It's a tool that changes the entire meaning of your sentence.

Here's the core idea in two short rules:

• Use "that" when the information is essential to identify the person or thing you're talking about. No commas.
• Use "which" when you are adding extra, non-essential information. Commas go around the clause.

That second type? That's a non-restrictive clause. The first type (with "that") is a restrictive clause.

Let me show you exactly how this works with a real-life example.

Why the Comma Changes Everything

Imagine you walk onto a used car lot. You say to the salesperson:

"I want the car that has the sunroof."

That sentence is restrictive. The clause "that has the sunroof" restricts which car you mean. If there are twenty cars, you need this information to find the right one. Without it, the sentence is incomplete.

Now imagine you already own a car. You're telling your friend about it:

"My car, which has a sunroof, is parked outside."

This is non-restrictive. The fact that your car has a sunroof is just an extra detail. You only have one car. The clause doesn't restrict anything; it just adds information. The commas here are like parentheses—they wrap up a "by the way" comment.

Do you feel the difference? In the first sentence, the listener knows there are many books. You're specifying a particular one. In the second sentence, the listener knows exactly which book you mean. The borrowing part is just background.

A Practical Test for Tricky Sentences

Not sure which one to pick? Here's a simple self-check.

Ask yourself: Does removing this clause destroy the meaning of the sentence?

• If yes → it's restrictive. Use that (and don't use commas).
• If no → it's non-restrictive. Use which (and add commas).

Let's test it.

Sentence A: "The restaurants that are cheap are popular."

Remove the clause: "The restaurants are popular." Hmm. That sounds like all restaurants are popular, which probably isn't true. The meaning shifted. So it's restrictive. Correct word: that.

Sentence B: "My local restaurants, which are cheap, are popular."

Remove the clause: "My local restaurants are popular." The meaning stays the same. We just lost a detail. So it's non-restrictive. Correct word: which.

The "Which" Exceptions People Forget

Now, a few honest confusions learners often face.

1. All "which" clauses need commas — almost always. There's one tiny exception. When "which" acts as a determiner (like "which car is yours?"), it's a question word, not a relative pronoun. That's a different beast entirely.

2. What about "that" with people? You can use "who" for people in restrictive clauses. "The woman who lives next door..." is fine. "That" also works for people informally, but "who" sounds cleaner.

3. British vs. American usage You'll sometimes see "which" used restrictively in British English without commas. Example: "The car which I drive is old." This is acceptable in the UK but considered non-standard in the US. If you're writing for an international audience, stick to the simpler rule: "that" for restrictive, "which" for non-restrictive.

Why This Matters in Real Writing

Using "which" and "that" correctly makes your writing sharper. More importantly, it prevents real misunderstandings.

Imagine a contract that says: "Employees who work overtime receive bonuses." That means only overtime workers get paid extra. Change it to "Employees, who work overtime, receive bonuses." Now it sounds like all employees work overtime, and all get bonuses. Different meaning.

The same logic applies to "which" and "that."

I remember a student once writing in a cover letter: "I led the project which was profitable." The hiring manager might think this person only led one project. If the student meant to specify a particular project among many, they should have written: "I led the project that was profitable."

A small word. A big difference.

Test Your Knowledge

Try this short practice. Fill in the blank with "that" or "which" (and add commas where needed).

1. The cake _____ she baked was delicious.
2. My grandmother _____ is a retired teacher loves gardening.
3. Cars _____ run on electricity are becoming common.

Answers:

1. that (restrictive — we're identifying which cake among possible cakes).
2. , which, (non-restrictive — you have one grandmother, teaching is extra detail).
3. that (restrictive — specifying electric cars among all cars).

Mastering this distinction is a small step, but it makes a big difference in how clear and professional your English sounds.

Want to check how well you understand relative clauses and other tricky grammar points? Take the free English grammar test at English Measure. It covers reading, listening, writing, and speaking — in just a few minutes you'll know your level. Start your free test here: Test Your English.

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