Many writers hesitate over which vs that because both words can introduce extra information about a noun. At first, they look almost interchangeable. However, the difference matters because each word can change the meaning of a sentence.
In most U.S. writing, use that when the information is essential. Use which when the information adds extra detail.
For example:
- The laptop that has the cracked screen needs repair.
- My laptop, which has a cracked screen, needs repair.
The first sentence identifies a specific laptop. The second sentence adds extra information about a laptop already known to the reader.
So, the choice is not just about grammar. It is also about meaning.
Quick Answer
Use that when the clause is essential to the meaning of the sentence.
- The files that include tax forms should be locked.
This means only the files with tax forms should be locked.
Use which when the clause gives extra information.
- The files, which include tax forms, should be locked.
This suggests all the files include tax forms.
In short, that usually identifies. Which usually adds. However, there is one useful caveat: which can sometimes appear in essential clauses, but that is often clearer in polished U.S. writing.
Why People Confuse Them
Both Words Can Point Back To A Noun
Writers confuse which and that because both words can refer to something already named.
For example:
- The jacket that I bought yesterday is too small.
- The jacket, which I bought yesterday, is too small.
Both sentences talk about a jacket. Still, they do not say the same thing.
The first sentence tells us which jacket. The second sentence adds a detail about the jacket.
Commas Add More Confusion
Another reason is punctuation. Many people learn “put a comma before which,” but that shortcut is incomplete.
A comma before which usually means the information is extra.
- My car, which needs gas, is parked outside.
Without the commas, the sentence may suggest that the clause identifies the noun.
Therefore, the better question is not “Should I use a comma?” The better question is “Is this information essential?”
Key Differences At A Glance
| Context | Best Choice | Why |
|---|---|---|
| The clause identifies the noun | that | The information is essential |
| The clause adds extra detail | which | The information is nonessential |
| The clause is surrounded by commas | which | Commas mark extra information |
| The clause has no commas and narrows the noun | that | This is usually clearer in U.S. writing |
| A preposition comes before the word | which | Use “in which,” “for which,” or “under which” |
| Casual speech | depends on meaning | People are often more flexible |
| Formal U.S. writing | that for essential, which for extra | This keeps meaning clear |
Compact Comparison
- That points to essential information.
- Which often points to extra information.
- That usually appears without commas in this use.
- Which often appears with commas when the detail is extra.
- Which also works after prepositions, as in “the rule under which we work.”
Meaning And Usage Difference
Use That For Essential Information
A clause with that usually tells the reader exactly which person, place, thing, or idea you mean.
- The students that missed the test must take it tomorrow.
This sentence does not mean all students must take the test tomorrow. Instead, it means only the students who missed it must do so.
Because the clause identifies the group, that works well.
Use Which For Extra Information
A clause with which usually adds information that the sentence can survive without.
- The test, which was scheduled for Monday, has been moved to Tuesday.
The main point is that the test has moved. The Monday detail adds context, but it does not identify which test.
As a result, which fits better.
Use The Removal Test
A simple test can help.
Remove the clause and ask whether the main meaning still works.
- The students must take it tomorrow.
- The test has been moved to Tuesday.
The first sentence feels incomplete because we do not know which students. Therefore, the clause is essential.
The second sentence still makes sense. So, the clause is extra.
Remember The Important Caveat
Although that is the better U.S. choice for essential clauses, which can sometimes appear in that role.
- The book which I borrowed from Maya is on my desk.
Many readers understand this sentence. Even so, this version is usually cleaner:
- The book that I borrowed from Maya is on my desk.
Therefore, use that for essential information unless you have a specific reason to choose which.
Tone, Context, And Formality
In Everyday Writing
In casual speech, people often use which and that more loosely. Most listeners still understand the meaning.
However, written English gives readers more time to notice structure. Because of that, the difference matters more in emails, reports, school papers, instructions, and articles.
In Formal U.S. Writing
For polished U.S. writing, that usually sounds cleaner in essential clauses.
- The proposal that includes the new budget is ready.
This tells the reader which proposal is ready.
Meanwhile, which works better when the information is extra.
- The proposal, which includes the new budget, is ready.
Here, the proposal is already known. The budget detail simply adds information.
When Which Sounds More Formal
Sometimes, which sounds more formal because it follows a preposition.
- Formal: The policy under which employees work has changed.
- More conversational: The policy that employees work under has changed.
Both sentences can be clear. However, the first sounds more formal, while the second sounds more natural in everyday writing.
Which One Should You Use?
Use That When The Detail Identifies
Choose that when the clause tells the reader which one you mean.
- The car that has the parking permit can stay in this lot.
- The form that you signed is missing a date.
- The shoes that I wear to work need new laces.
In each sentence, the clause identifies a specific noun.
Use Which When The Detail Adds
Choose which when the clause gives extra information.
- My car, which has a parking permit, can stay in this lot.
- The form, which you signed yesterday, is missing a date.
- My work shoes, which need new laces, are by the door.
Here, the nouns are already clear. The which clauses only add details.
Use Which After A Preposition
When a preposition comes before the relative word, use which.
- the process by which we review applications
- the rule under which the team works
- the reason for which the refund was denied
You would not write “by that,” “under that,” or “for that” in these structures.
When One Choice Sounds Wrong
Comma Plus That Often Sounds Wrong
A comma usually signals extra information. Because of that, that often sounds wrong after a comma in this kind of sentence.
- Awkward: My phone, that I bought last year, still works.
- Better: My phone, which I bought last year, still works.
The second sentence sounds smoother because which matches the extra-information structure.
That Sounds Wrong After A Fronted Preposition
Do not use that after a fronted preposition.
- Awkward: The issue about that we spoke is resolved.
- Better: The issue about which we spoke is resolved.
In everyday speech, you could also write:
- The issue that we spoke about is resolved.
That version sounds more natural and less formal.
Which Can Sound Less Clear In Essential Clauses
Sometimes, which is grammatical but not ideal.
- Less clear: The files which contain tax forms are locked.
- Clearer: The files that contain tax forms are locked.
The second sentence is easier to process because that clearly marks essential information.
Common Mistakes And Quick Fixes
Mistake 1: Using Which When That Is Clearer
- Weak: The password which opens the admin account has changed.
- Better: The password that opens the admin account has changed.
The clause identifies the password. Therefore, that is clearer.
Mistake 2: Forgetting Commas With Extra Information
- Weak: The office printer which is near the kitchen is broken.
- Better: The office printer, which is near the kitchen, is broken.
If there is only one office printer, the location is extra. So, use commas.
Mistake 3: Adding Commas Around Essential Information
- Weak: The employees, that work weekends, get shift pay.
- Better: The employees that work weekends get shift pay.
The corrected sentence means only weekend workers get shift pay.
Mistake 4: Treating Every Which As Extra
Not every which needs a comma.
- Possible: The question which bothered me most was about rent.
- Often clearer: The question that bothered me most was about rent.
The second version is usually better in U.S. edited writing.
Mistake 5: Fixing The Word Before Fixing The Meaning
Do not swap which and that without checking the meaning first.
- The apartments that allow pets cost more.
- The apartments, which allow pets, cost more.
The first sentence means only some apartments allow pets. The second suggests all the apartments allow pets.
Everyday Examples
Work Examples
- The report that includes the sales numbers is ready.
- The report, which includes the sales numbers, is ready.
The first sentence identifies one report. The second adds extra information about a report already known.
Email Examples
- Please resend the email that has the attachment.
- Please resend the email, which has the attachment.
The first sentence asks for a specific email. The second adds a detail.
School Examples
- The assignment that is due Friday counts for half the grade.
- The assignment, which is due Friday, counts for half the grade.
The first sentence identifies the assignment. The second adds the due date.
Home Examples
- The drawer that sticks is the one on the left.
- The drawer, which sticks, is the one on the left.
The first sentence suggests more than one drawer. The second adds a detail about one drawer.
Food Examples
- The meals that contain dairy are marked on the menu.
- The meals, which contain dairy, are marked on the menu.
The first sentence means only some meals contain dairy. The second suggests all the meals contain dairy.
Dictionary-Style Word Details
Verb
- Which: Which is not commonly used as a verb in modern English. In this comparison, it works mainly as a pronoun or determiner.
- That: That is not commonly used as a verb in modern English. In this comparison, it works mainly as a relative pronoun.
Therefore, the verb category does not meaningfully apply to either word.
Noun
- Which: Which is not normally used as a noun in everyday grammar. You can talk about the word itself, as in “the word which,” but that is not its normal role.
- That: That is also not normally used as a noun in this comparison. You can mention it as a word, but it does not act as a regular noun here.
So, the noun category has limited value for this topic.
Synonyms
Exact synonyms do not work well here because which and that are function words.
- Which: Closest plain alternatives may include “the one that,” “the thing that,” or sometimes “what,” depending on the sentence.
- That: Closest plain alternatives may include “the one,” “the thing,” or no word at all in some clauses.
For example:
- The book that I bought was expensive.
- The book I bought was expensive.
In this case, that can disappear. However, that does not mean every use of that can be removed.
Also, do not force antonyms. These words do not have useful opposites in this comparison.
Example Sentences
- Which: The meeting, which starts at noon, will be short.
- Which: The rule under which we filed the claim has changed.
- Which: She missed the bus, which made her late for class.
- That: The meeting that starts at noon will be short.
- That: The claim that we filed last week was approved.
- That: The bus that stops near my house runs late.
Together, these examples show the main pattern. That identifies. Which often adds extra detail.
Word History
- Which: Which comes from older English forms linked to asking or identifying “which one” or “of what kind.”
- That: That also comes from older English forms used for pointing, identifying, and connecting ideas.
This history can be interesting. Still, it should not decide your modern word choice. Meaning and sentence structure matter more.
Phrases Containing
- Which: Common phrases include “which is which,” “in which case,” “which is to say,” and “every which way.”
- That: Common phrases include “that is,” “that’s that,” “all that,” “at that,” “be that as it may,” and “having said that.”
These phrases are useful, but they do not control the main which vs that rule.
FAQ
Is which ever correct without commas?
Yes. Which can appear without commas when it introduces essential information.
- The book which I ordered arrived today.
However, many U.S. editors would prefer:
- The book that I ordered arrived today.
So, which without commas is not always wrong. Still, that is often clearer.
Should I always put a comma before which?
No. Use a comma before which when the clause adds extra information.
- My car, which needs gas, is parked outside.
However, do not add a comma if the clause is essential.
- The option which costs less may not include delivery.
Even here, many U.S. writers would choose that.
Can I use that after a comma?
Usually, no. In this type of clause, comma plus that sounds unnatural.
- Awkward: My laptop, that I bought in 2023, still works.
- Better: My laptop, which I bought in 2023, still works.
Can that be left out?
Sometimes, yes.
- The show that we watched was funny.
- The show we watched was funny.
Both versions sound natural.
However, do not remove that when the sentence becomes unclear.
Is which more formal than that?
Sometimes, but not always.
Which can sound more formal after a preposition.
- the policy under which we work
However, that is not automatically casual, and which is not automatically formal. The sentence structure matters most.
Which one is better for U.S. business writing?
Use that for essential information.
- The file that contains the contract is encrypted.
Use which for extra information.
- The file, which contains the contract, is encrypted.
This pattern keeps business writing clear.
Does the wrong choice change the meaning?
Yes, it can.
- The apartments that allow pets cost more.
- The apartments, which allow pets, cost more.
The first sentence means only pet-friendly apartments cost more. The second suggests all the apartments allow pets.
What Is The Fastest Way To Choose?
Ask one question: “Do I need this information to identify the noun?”
If yes, use that.
- The receipt that shows the refund is in my email.
If no, use which with commas.
- The receipt, which shows the refund, is in my email.
Conclusion
The difference in which vs that comes down to meaning. Use that when the information identifies the noun. Use which when the information adds extra detail and is usually set off with commas.
Also, remember the nuance. Which can sometimes introduce essential information, but that is often clearer in polished U.S. writing.
When in doubt, use the removal test. If the sentence loses key meaning without the clause, choose that. If the sentence still works and the clause only adds detail, choose which.
