Which vs. That
The safest choice depends on clause type and style. “That” introduces defining/restrictive relative clauses; “which” can introduce defining clauses in general and British usage, and it is also the standard choice for non-defining clauses set off by commas. Many American editorial styles prefer “that” for restrictive clauses and “which” for nonrestrictive ones.
For a non-defining clause that adds extra information, use “which” with commas. For a defining clause, “that” is a safe choice—especially in American edited prose—but “which” is also grammatical in defining clauses in broader English usage. Style and region therefore matter.
Key details
Choose the right form
| Context | Use | Decision |
|---|---|---|
| non-defining clause adding extra information | which + commas | Use “which” for the standard non-defining construction. |
| defining/restrictive clause in American edited prose | that often preferred | “That” is a safe choice under many US editorial styles. |
| defining/restrictive clause in broader English usage | that or which | “Which” is also grammatical in defining clauses, especially outside styles that impose the US editorial preference. |
Quick tests
Decision test
Is the relative clause non-defining and set off as extra information?
If yes: Use “which” with commas.
If no: For a defining clause, “that” is a safe US-edited choice, but “which” is also grammatical in broader English usage.
Caveat: This is partly a clause-type distinction and partly a style/regional preference; do not present “which” in every restrictive clause as ungrammatical.
Examples
The report, which was published on Monday, is already being revised.
The comma-delimited clause is non-defining, so “which” is standard.
The report that contains the revised figures is on my desk.
“That” introduces a defining clause and fits common American editorial preference.
The report which contains the revised figures is on my desk.
“Which” can also introduce a defining clause in broader English usage.
Further guidance
Clause Type First
Determine whether the relative clause identifies which person/thing you mean (defining/restrictive) or merely adds extra information (non-defining/nonrestrictive).
Defining
Cambridge allows “which” or “that” for things in defining clauses. MLA editorial guidance prefers “that” for restrictive clauses, and Chicago likewise presents that/which as its edited-US distinction while acknowledging restrictive “which,” especially in British English.
Non Defining
Cambridge states that “that” is not used to introduce non-defining relative clauses; “which” is used for things and these clauses are punctuated with commas.
Style And Region
This is not well represented by a universal red/green grammar rule. A restrictive “which” may be grammatical while still being changed to “that” under a particular American house style.
Sources and evidence
Sources are shown with the role they play in this guide. Historical or style-sensitive claims are kept within the evidence boundary described above.
- Relative clauses: defining and non-defining — Cambridge Grammar (opens in a new tab)Cambridge University Press · British/general English relative-clause behavior
- On Witches and Whiches: A Guide to Restrictive and Nonrestrictive Clauses (opens in a new tab)MLA Style Center / Modern Language Association · MLA editorial distinction between restrictive that and nonrestrictive which
- Which vs. That — Chicago Q&A (opens in a new tab)The Chicago Manual of Style / University of Chicago Press · Chicago preference and British-English caveat