Quick Answer
“Which” doesn’t have a true synonym, because it’s a grammar function word, not a content word like happy or fast. What it does have is a set of alternatives that work in specific situations: what (in questions), that or who (in relative clauses), and whichever (when talking about a choice among options). The right substitute depends entirely on the job “which” is doing in the sentence.
Correct: The book that I borrowed is overdue. (restrictive clause) Also correct: The book, which I borrowed last week, is overdue. (nonrestrictive clause) Incorrect in formal American English: The book which I borrowed is overdue. (using “which” without a comma for essential information)
What Does “Which” Mean and What Part of Speech Is It?
“Which” can function as a pronoun or a determiner, and it changes job depending on the sentence.
Which as a Relative Pronoun
As a relative pronoun, “which” connects a clause back to a noun already mentioned. Example: My laptop, which is three years old, still runs fine. Here “which” refers back to “laptop” and introduces extra information about it.
Which as an Interrogative Pronoun
As an interrogative pronoun, “which” is used to ask someone to choose from a known set of options. Example: Which of these two shirts do you like better? Unlike “what,” which asks about something open-ended, “which” usually implies the choices are already on the table.
Which as a Determiner
“Which” can also sit directly in front of a noun to ask about a specific option: Which train goes to downtown? Here it modifies “train” rather than standing in for it.
Is There a Real Synonym for “Which”?
Not exactly. Content words like “difficult” have close synonyms such as “hard” or “challenging” because they describe a quality. “Which” doesn’t describe anything — it performs a grammatical function, so its replacements aren’t interchangeable synonyms but context-specific substitutes. Swapping “which” for “that,” “what,” or “who” changes the sentence’s meaning or formality, so the choice always depends on what role the word plays.
How to Choose the Right Alternative to “Which” by Context
Formal and Academic Writing
In careful, formal writing, use “that” for essential (restrictive) information and “which” for extra (nonrestrictive) information set off by commas.
Example: The proposal that includes a budget breakdown was approved.
Informal and Conversational Use
In everyday speech, many people use “that” or drop the relative pronoun entirely instead of “which.”
Example: The show I watched last night was great. (no relative pronoun needed)
Asking Questions
Use “what” when the options are unknown or unlimited, and “which” when you’re choosing from a specific, known set.
Example: What do you want for dinner? / Which of these two restaurants do you want to try?
Introducing Extra Information (Nonrestrictive Clauses)
Use “which,” always with a comma, when the clause adds a detail that could be removed without changing the sentence’s core meaning.
Example: The report, which took two weeks to finish, impressed the board.
Introducing Essential Information (Restrictive Clauses)
Use “that,” without a comma, when the clause is needed to identify exactly what you’re talking about.
Example: The email that mentions the deadline is still in my inbox.
Alternatives to “Which,” Grouped by Use
Interrogative Alternatives
- What — for open-ended questions: What time works for you?
- What kind of — for asking about category or type: What kind of car did you buy?
Relative Clause Alternatives
- That — for restrictive clauses about things: The chair that broke needs fixing.
- Who — for restrictive or nonrestrictive clauses about people: The manager who hired me just retired.
- Whom — for people in the object position, mostly in formal writing: The client, whom we met yesterday, signed the contract.
Choice-Among-Options Alternatives
- Whichever — for an open choice among options: Take whichever seat is free.
- Whatever one — a more casual version of “whichever”: Grab whatever one you like.
- Any of — when any option is acceptable: You can pick any of these colors.
Formal Phrase Alternatives
- In which — often replaceable with “where” for places: the city in which she was born / the city where she was born
- By which — sometimes replaceable with “how”: the method by which it was made
- At which point — can shorten to “when” in casual writing: at which point I left / when I left
“Which” vs. Similar Words
Which vs. That
Both can introduce a clause about a thing, but formal American English reserves “that” for essential information and “which” for extra information set off by commas. “That” clauses have no commas; “which” clauses do.
The car that has a dent is mine. (identifies which car) My car, which has a dent, is parked outside. (adds extra detail about the one car already identified)
Which vs. What
“Which” asks about a choice from a known or implied set; “what” asks a more open question. Compare: Which color do you want, red or blue? versus What color do you want?
Which vs. Who/Whom
“Which” refers to things or animals without names; “who” and “whom” refer to people (and sometimes named animals). The dog, which was barking loudly, woke the neighbors versus The neighbor who complained called the landlord.
Which vs. Whichever
“Which” typically asks a direct question or introduces a specific clause. “Whichever” means “no matter which one” and signals an open choice: Whichever route you take, you’ll arrive on time.
Which vs. Either
“Either” refers to one of exactly two options and often implies no preference: You can take either road. “Which” is used to ask someone to specify, regardless of how many options exist.
British vs. American English: Does “Which” Ever Replace “That”?
Yes. In British English, “which” is commonly used for both restrictive and nonrestrictive clauses, and the strict that/which split taught in American style guides is followed less consistently. American style guides such as those used in US academic and business writing tend to enforce the that/which distinction more strictly, reserving “which” for nonrestrictive clauses. Neither approach is wrong; they simply reflect different regional conventions.
Can You Start a Sentence With “Which”?
Yes, but mainly in two situations: asking a direct question (Which one do you prefer?) or, in more casual or literary writing, continuing a thought from the previous sentence for stylistic effect. In formal writing, starting a new sentence with “which” as a relative pronoun (without an antecedent in the same sentence) is usually considered a fragment and should be avoided.
Common Phrases and Expressions With “Which”
“Which is to say” — used to rephrase or clarify a previous statement. She’s fluent in three languages, which is to say she picks up new ones quickly.
“Which brings us to” — used to transition to a related point. Sales dropped last quarter, which brings us to our next agenda item.
“In which case” — used to describe a resulting scenario. He might be late, in which case we’ll start without him.
“Of which” — used in formal writing to avoid ending a sentence with a preposition. The committee, the members of which were all volunteers, met monthly.
“At which point” — used to mark a moment in a sequence. The line grew longer, at which point we decided to leave.
“Which” in Real-Life Sentences: School, Work, Writing, and Conversation
School
Which chapter should we review before the test?
Workplace
The client sent two proposals, which I’ve attached for your review.
Writing
The novel, which was published in 1997, is still widely read today.
Conversation
I have two options — not sure which one to pick.
Common Mistakes to Avoid With “Which”
Using “Which” for People Incorrect: The employee which finished first got a bonus. Correct: The employee who finished first got a bonus. Explanation: “Which” refers to things, not people — use “who” instead.
Using “Which” for Restrictive Clauses in Formal American English Incorrect: The file which you need is on the desktop. Correct: The file that you need is on the desktop. Explanation: Since the clause identifies which specific file, it’s restrictive and calls for “that” in formal American usage.
Confusing “Which” and “What” in Questions Incorrect: Which do you want to eat tonight? (with no options mentioned) Correct: What do you want to eat tonight? Explanation: Use “what” when the choices haven’t been narrowed down; use “which” when specific options are already on the table.
Missing Commas Around Nonrestrictive “Which” Clauses Incorrect: My phone which is nearly new stopped working. Correct: My phone, which is nearly new, stopped working. Explanation: Nonrestrictive “which” clauses always need commas on both sides.
Overusing “Which” When “That” Sounds More Natural Incorrect: This is the project which I mentioned earlier. Correct: This is the project that I mentioned earlier. Explanation: In casual and business writing, “that” often reads more naturally for restrictive clauses than “which.”
Quick Practice: Choose the Right Word
- The laptop ___ I bought last month already has a scratch. (that / which)
- ___ movie do you want to watch, this one or that one? (What / Which)
- My sister, ___ lives in Chicago, is visiting next week. (that / which)
- Take ___ umbrella is closest to the door. (whichever / whatever)
- The employee ___ won the award thanked her team. (which / who)
- Correct this sentence: The report which needs your signature is on your desk.
- Correct this sentence: My car which broke down is at the shop.
- Fill in the blank: She couldn’t decide ___ dress to wear. (what / which)
Frequently Asked Questions
Is “which” a pronoun or a conjunction? “Which” is a pronoun, not a conjunction. It functions as a relative pronoun when it links a clause back to a noun, and as an interrogative pronoun when it asks a question. It can also act as a determiner directly before a noun, as in “which train.”
What’s the difference between “which” and “that”? “That” introduces restrictive clauses that identify exactly what’s being talked about, with no commas. “Which” introduces nonrestrictive clauses that add extra, removable detail, and it’s set off by commas in formal American English.
Can “which” refer to a person? No. “Which” refers to things, animals, or groups, not individual people. Use “who” or “whom” for people.
Is it correct to start a sentence with “which”? It’s correct when asking a direct question, like “Which one is yours?” As a relative pronoun continuing a previous idea, starting a sentence with “which” is usually seen as a fragment in formal writing.
Is “which” used for restrictive or nonrestrictive clauses? Both are possible, but formal American style guides recommend “which” only for nonrestrictive clauses and “that” for restrictive ones. British English is more flexible about using “which” for both.
What’s another word for “in which”? “Where” often works as a simpler substitute when referring to a place, as in “the town in which I grew up” versus “the town where I grew up.”
Is “whichever” the same as “which”? Not quite. “Whichever” means “no matter which one” or “any one you choose,” while “which” typically asks for a specific choice or introduces a clause about something already identified.
Do British and American English treat “which” differently? Yes. American style guides more strictly separate “that” (restrictive) from “which” (nonrestrictive). British English commonly uses “which” for both types of clauses.
When should you use “what” instead of “which”? Use “what” when the possible answers are open-ended or unknown. Use “which” when you’re choosing among a specific, limited set of options.
Do you need a comma before “which”? Yes, when “which” introduces a nonrestrictive clause adding extra information. No comma is needed if “which” is used as an interrogative pronoun starting a question.
Is there a true synonym for “which,” or only substitutes? Only substitutes. Because “which” is a function word rather than a content word, its replacements depend on the grammatical role it’s playing, not on shared meaning.
Key Takeaways
“Which” doesn’t have one-size-fits-all synonyms — the right substitute depends on whether you’re asking a question (“what”), identifying something essential (“that”), describing a person (“who”), or offering an open choice (“whichever”). Remember the comma rule: no comma with “that” for essential details, a comma with “which” for extra ones. Getting that distinction right solves most “which” confusion on its own.
Practice Answer Key
- that — the clause identifies which specific laptop, so it’s restrictive.
- Which — two specific options are already mentioned.
- which — the sister is already identified by name relation; this is extra detail, so it needs commas.
- whichever — signals an open choice, not a specific question.
- who — refers to a person.
- Corrected: The report that needs your signature is on your desk.
- Corrected: My car, which broke down, is at the shop.
- which — implies she’s choosing between specific dresses already available to her.
