Which vs. that: When to use each?

Key takeaways:

Use “that” for essential clauses necessary to a sentence's meaning.
Employ “which” in non-essential clauses that offer more details.
Commas are often a clue: “which” clauses are set off by commas, while “that” clauses are not.

Part of the series Grammar Debugged—English for Devs

The words “which” and “that” are both used to introduce clauses, but they have different rules and purposes. “That” is used for essential clauses that provide the necessary information, while “which” is used for non-essential clauses that add extra detail. This Answer will explain when and how to use “which” and “that” correctly in your writing.

When to use that

“That” is used to introduce restrictive clausesA restrictive clause is essential to the meaning of the sentence. It defines or identifies the noun it modifies, and without it, the sentence would lose its intended meaning. Restrictive clauses are not set off by commas., also known as essential clauses. These clauses provide crucial information that defines or limits the meaning of the sentence.

Examples:

“The book that I borrowed from the library is overdue.” (There are multiple books, and the phrase specifies which one is due.)
“Books that teach critical thinking are essential for high school students.” (In this context, the sentence is specifically talking about only those books that teach critical thinking.)

Tip: If removing the clause changes the sentence's meaning, use “that.”

When to use which

“Which” introduces non-restrictive clausesA non-restrictive clause provides extra, non-essential information about the noun. This information could be removed without changing the core meaning of the sentence. Non-restrictive clauses are set off by commas., also known as non-essential clauses. These clauses add extra information that isn’t necessary to understand the main point of the sentence.

Examples:

“The book, which I borrowed from the library, is overdue.” (There’s only one book in the context, and the fact that it came from the library is just extra info—making the sentence interesting but not really required.)
“Books, which are a great source of knowledge, can shape our thinking.” (The fact that books are a great source of knowledge is extra information and not essential to the sentence’s core meaning.)

Tip: “Which” clauses are often separated by commas.

Quick test

Choose the correct word (which or that) for each sentence:

The car _____ he bought last week is already having issues.

Using which for essential clauses

Incorrect: “The car, which is parked outside, belongs to him.” (Implies that the car being parked outside is extra information, but that was not the intent here.)
Correct: “The car that is parked outside belongs to him.” (Clarifies that the specific car being referred to is the one parked outside.)

Using that for non-essential clauses

Incorrect: “Her dress that is red is beautiful.” (Implies she has multiple dresses, and the red one is being specified.)
Correct: “Her dress, which is red, is beautiful.” (The phrase which is red adds extra detail, because we already know which dress is being discussed.)

Ignoring commas for which clauses:

Incorrect: “The pen which is on the table is mine.”
Correct: “The pen, which is on the table, is mine.” (Since “which is on the table” is additional information, a comma is needed.)

Frequently asked questions

Haven’t found what you were looking for? Contact Us

What is the rule for using “that” or “which”?

“That” is used to introduce essential information that defines or limits the noun it modifies. It’s used in restrictive clauses, which are not set off by commas.
- Example: “The book that I borrowed from the library is overdue.”(This specifies which book is overdue.)
“Which” is used to introduce non-essential, additional information about the noun. It’s used in non-restrictive clauses, which are set off by commas.
- Example: “The book, which I found very interesting, is about ancient history.“ (The information about the book being interesting is extra.)

When should you use each?

“Each” is used to refer to every single member of a group individually.

Example: “Each student received a certificate.”
Example: “The runners crossed the finish line one by each.”

Where do we use “which” and “that”?

“Which” and “that” are both used to introduce clauses that modify nouns.
“Which” is for non-essential information (commas).
“That” is for essential information (no commas).

Where do we use each?

“Each” is used to refer to every single member of a group when considering them individually.

Can you use “which” and “that” interchangeably?

No, they are used differently:

“That” introduces restrictive clauses (essential to the meaning of the sentence).
“Which” introduces non-restrictive clauses (providing extra, non-essential information).

How do you use commas with “which” and “that”?

That: No commas.
Example: The book that you lent me was great.
Which: Use commas.
Example: The book, which was quite interesting, is on the shelf.

What’s an easy way to remember how to use “which” vs. “that”?

That: essential (no commas).
Which: extra information (use commas).

If you can remove the clause and the sentence still makes sense, use “which.” If removing it changes the meaning, use “that.”

Word	Meaning	Examples
That	Introduces essential (restrictive) clauses.	"The house that has a red roof is ours." (Defines which house.)
Which	Introduces non-essential (non-restrictive) clauses.	"The house, which has a red roof, is ours." (Extra detail about the house.)