Choosing between that and which becomes easier once you decide whether the following clause identifies the noun or merely adds extra information. In careful US writing, that usually introduces an essential, restrictive clause. Which usually introduces a nonessential, nonrestrictive clause set off by commas.
The distinction is useful because punctuation and word choice can change what a sentence claims. Still, the rule has some nuance: which can also introduce a restrictive clause in standard English, although many American editors and house styles prefer that in that position.
Quick Answer
Use that for a restrictive clause that identifies or limits the noun. Do not place a comma before it.
Use which for a nonrestrictive clause that adds removable information. Set that clause off with commas.
For polished US prose, this is the safest pattern:
- The files that contain signatures are confidential.
- The files, which contain signatures, are confidential.
The first sentence refers only to files containing signatures. The second suggests that all the files contain signatures.
Why People Confuse Them
Both words can connect a noun to a relative clause, and both often refer to things rather than people. In speech, listeners also rely on pauses and context, so an imprecise choice may pass unnoticed.
Confusion grows because some grammar references accept which in restrictive clauses, while many US style guides teach a clean division: that for essential information and which for extra information. The difference is partly grammar, partly punctuation, and partly editorial preference.
Key Differences At A Glance
| Context | Best Choice | Why |
|---|---|---|
| The clause identifies which item you mean | that | The information restricts the noun |
| The clause adds an aside | which | The information is nonessential |
| A comma comes before the relative clause | which | Commas normally mark added information |
| No comma appears before an essential clause | that | This is the preferred US pattern |
| A preposition comes directly before the word | which | Standard English allows “in which,” not “in that” |
| A restrictive clause must follow a strict house style | that | Many US editors reserve restrictive “which” |
Meaning and Usage Difference
As relative words, that and which introduce clauses that describe a noun. The key question is whether the clause narrows the noun’s identity.
| Feature | that | which |
| Usual US role | Restrictive clause | Nonrestrictive clause |
| Information | Essential or identifying | Extra or parenthetical |
| Commas | Usually none | Usually required around the clause |
| Restrictive use | Standard and widely preferred | Grammatical, but sometimes edited to “that” |
| After a fronted preposition | Not used | Used: “under which” |
A restrictive clause selects a subset: “The chairs that have cushions are reserved.” Only the cushioned chairs are reserved.
A nonrestrictive clause comments on an already identified noun: “The conference room chairs, which have cushions, are reserved.” The sentence presents the cushioning as extra information about those chairs.
Tone, Context, and Formality
The choice usually changes precision, not emotional tone. That often sounds direct because it tightly links the noun to essential information. Which often creates a brief parenthetical pause because commas separate its clause from the main statement.
In formal US business, academic, and edited writing, the traditional division remains a dependable choice. In less formal writing, restrictive which may sound natural and remains grammatical. However, a publication may still replace it with that for consistency.
Which One Should You Use?
First, remove the clause mentally.
If removing it changes which person or thing the sentence identifies, the clause is restrictive. Use that without commas:
“The warranty that covers accidental damage costs more.”
If removing it leaves the main identification intact, the clause is nonrestrictive. Use which with commas:
“The extended warranty, which covers accidental damage, costs more.”
Use which when a preposition must come before the relative word:
“The policy under which we operate expires in June.”
You could rewrite that sentence as “The policy that we operate under expires in June,” but you cannot write “under that” in the same structure.
When One Choice Sounds Wrong
That sounds wrong in a nonrestrictive clause:
Incorrect: “Our main office, that opened in 2019, is moving.”
Better: “Our main office, which opened in 2019, is moving.”
A comma before that is therefore a strong warning sign.
Which may sound wrong to readers who follow strict American editorial conventions when it introduces an ordinary restrictive clause:
Acceptable but less preferred in some US settings: “The report which explains the delay is attached.”
Safer US edit: “The report that explains the delay is attached.”
Common Mistakes (and Quick Fixes)
A common mistake is choosing the word before deciding the meaning. Decide whether the clause limits the noun first; then choose the word and punctuation.
Another mistake is adding a comma automatically before every which. Restrictive which does not take a comma: “The route which avoids downtown is faster.” Many US editors would prefer that, but the comma depends on meaning.
Writers also place that after a fronted preposition. Replace “the process by that we measure results” with “the process by which we measure results,” or move the preposition: “the process that we measure results by.”
Everyday Examples
- Please upload the receipt that shows the order number.
- My receipt, which is slightly torn, is still readable.
- The bus that stops near the library arrives at 8:10.
- Route 12, which stops near the library, runs every half hour.
- We need a charger that works with this laptop.
- This charger, which came with the laptop, no longer works.
- The agreement under which the team operates ends Friday.
- The apartment that faces the park has already been rented.
Dictionary-Style Word Details
Verb
- that: Not used as a verb in standard US English.
- which: Not used as a verb in standard US English.
Noun
- that: Not normally classified as a noun. In this comparison, it functions as a relative word introducing a clause.
- which: Not normally classified as a noun. In this comparison, it functions as a relative or interrogative word, depending on the sentence.
Synonyms
Neither word has a true synonym that works in every structure.
- that: In some restrictive clauses, which is a grammatical alternative, though US editors may prefer that.
- which: In nonrestrictive clauses, that is not a standard substitute. With a fronted preposition, which is also required from this pair.
There are no useful antonyms for these grammatical uses.
Example Sentences
- that: “The package that arrived this morning belongs to Mia.”
- which: “Mia’s package, which arrived this morning, is on the counter.”
The first clause identifies the package. The second adds information about a package already identified as Mia’s.
Word History
Both words have long histories in English and developed several grammatical roles over time. Their modern division in relative clauses did not arise because they originally had completely separate meanings. The strict US preference for restrictive that and nonrestrictive which is a later editorial convention, not a complete description of every standard use.
Phrases Containing
- that: “that is,” “that said,” “so that,” and “the one that”
- which: “which one,” “in which,” “for which,” and “the one which”
Not every phrase above involves a relative clause, so the restrictive-versus-nonrestrictive rule does not apply to every appearance of either word.
FAQs
No. That is the preferred choice for ordinary restrictive clauses in much edited US writing, but which can also be grammatical. Follow that when you want the clearest American convention or when a publisher, school, or workplace requires that distinction.
Yes. Which can introduce a restrictive clause without commas, especially in usage that does not follow the strict American editorial preference. Even so, changing it to that often makes the sentence easier for US readers and prevents a style correction.
No. Which needs commas when it begins a nonrestrictive clause that adds removable information. It takes no comma when the clause is restrictive. It also appears without this clause pattern in questions and phrases such as “which option” or “under which policy.”
Usually not when that introduces a relative clause. A restrictive that clause connects directly to the noun without a comma. When the information is parenthetical and needs commas, use which instead. Other sentence structures may place punctuation near that for unrelated reasons.
Sometimes. You may often omit that when it acts as the object inside a restrictive clause: “The laptop I ordered arrived.” Do not omit it when it acts as the subject: “The laptop that arrived is mine” needs the relative word.
Yes. The choice often works with commas to show whether a description limits a group or comments on the whole group. “Cars that need repairs” means only some cars; “cars, which need repairs,” presents all the identified cars as needing repairs.
Conclusion
For clear US writing, use that to introduce essential information without commas and which to introduce extra information with commas. This pattern makes meaning visible at a glance.
Remember the nuance: restrictive which can be grammatical, but many American editors prefer that. Nonrestrictive clauses, however, normally require which. Decide what the clause means before choosing the word, and let the punctuation reflect that decision.
