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
| Clause/context | Safe choice | Punctuation | Style/region caveat |
|---|---|---|---|
| non-defining information about a thing | which | commas around the clause | “That” is not used here in standard guidance. |
| defining/restrictive clause in edited US prose | that | normally no commas | MLA/Chicago-style editing commonly prefers this distinction. |
| defining/restrictive clause in broader English usage | which or that | normally no commas | Cambridge documents defining “which”; restrictive “which” is common in British English. |
| relative clause referring to a whole preceding clause | which | usually set off from the main clause | Cambridge uses “which,” not “that,” for this function. |
Decide restrictive vs. nonrestrictive meaning before choosing punctuation. The comma is not merely decorative; it changes how the clause is interpreted.
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