Comma before “which” vs. “that”: Rules, Examples, and Clear Writing Tips

How Are “Which” and “That” Different?

 Writers sometimes have a hard time telling when to use which or that. Both words start new clauses in a sentence, but they are not interchangeable. Picking the correct word depends on what you want to do grammatically.

A restrictive clause limits or defines the meaning.

A nonrestrictive clause adds information that can be left out without affecting core meaning.

that → a restrictive, defining, or essential clause

which → a nonrestrictive, non-defining, or extra clause (usually after a comma)

Knowing the distinction will help you write clearer, tighter, and more professional sentences.

Why Does It Matter?

 Knowing when to use which or that is not just a grammar nitpick—it's a matter of clarity, precision, and reader comprehension.

1. Using the wrong word or grammar can change the sentence’s meaning.

A restrictive clause doesn’t just add information—it changes what the noun refers to. Use the wrong word and you may confuse the reader or even change the point you’re trying to make.

2. Academic, professional, journalistic, and business writing expects it.

Universities, journals, business style guides (including The New York Times) follow U.S. formal standards, and strongly prefer:

that for restrictive clauses

which for nonrestrictive clauses

3. It makes writing more readable.

Correct use of clauses makes it easier for readers to process complex, detailed information logically, which is why it’s extra important in technical, academic, and formal writing.

When to Use “Which” vs. “That”

 Here are some simple rules for when it’s correct to use which or that, along with examples.

1. Use that for restrictive (essential/defining) clauses

A restrictive clause limits or identifies the noun it’s referring to. If you remove a restrictive clause, the meaning of the sentence changes.

Examples:

The laptop that you ordered is out of stock.

The prize that I won was $100.

The team that arrives last will be disqualified.

2. Use which for nonrestrictive (extra/non-defining) clauses — with a comma

A nonrestrictive clause is non-essential and can be omitted without affecting the meaning of the sentence.

Examples:

The laptop, which you ordered, is out of stock.

The prize, which I won, was $100.

The team, which arrived last, was disqualified.

3. Use which for explanations or clarifications

Whenever you want to add descriptive detail or commentary, which is the only appropriate choice.

Examples:

He was fired, which was shocking.

The results were delayed, which caused problems.

4. Use that to define categories or types

Whenever the sentence is stating a specific category, use that.

Examples:

Foods that contain flour must be labeled as such.

Items that contain gold must be x-rayed.

5. Use which to refer to an entire preceding clause

When you want to comment on the sentence as a whole, use which.

Examples:

She collaborated with the enemy, which is shocking.

The pronunciation was misheard, which caused confusion.

6. In U.K. English, “which” may be used in restrictive clauses

U.K. style is less strict, and allows you to use which without a comma, even in restrictive clauses.

Examples (U.K. style):

The book which won this year’s prize is brilliant.

The team which performed best ultimately won.

However, in U.S. style, using that in the same sentences is always preferable.

“Which” vs. “That” Sentence Examples

 Here are some examples that show how the meanings of restrictive and nonrestrictive clauses change depending on which word you use.

Restrictive (that)

The dogs that are at the shelter need new homes.

The cars that are recalled need to be repaired.

The email that you sent had the wrong link.

Nonrestrictive (which)

The dogs, which are at the shelter, need new homes.

The cars, which are recalled, need to be repaired.

The email, which you sent, had the wrong link.

(Implies that all the dogs need homes.)

(Implies that all the cars need repairs.)

(Adds extra information about the sender.)

“Which” vs. Similar Concepts

Common Mistakes & Writing Tips

❌ Mistake 1: Using which without a comma in U.S. English

Fix: Add a comma or use that.

Incorrect: The rule which governs the award is strict.

Correct: The rule that governs the award is strict.

❌ Mistake 2: Using that for nonrestrictive/non-defining/extra clauses

Incorrect: The book that I borrowed yesterday, is great.

Correct: The book, which I borrowed yesterday, is great.

❌ Mistake 3: Overusing “which” in formal/academic/professional writing

Academic style prefers that for most restrictive clauses.

Be consistent within the same document.

✔ Writing Tips

●  Sentence needs the clause — use that.

●  Pull out the clause: If the sentence still makes sense, use which.

●  Always check punctuation—it’s often a comma that chooses which word is correct.

●  U.K. style is looser, but clarity is still king.

Conclusion

 “Which” and “that” are small words, but using them logically is an important part of clear, grammatical writing.

that for restrictive, essential information, and which (with a comma) for extra, nonessential detail. Understanding this distinction helps you write more professional, accurate, and readable sentences—whether you’re writing academic papers, business emails, reports, or blog content.

Follow the rules and examples in this guide, and you’ll be able to choose the correct word every time.