which

1.determinerA2

Definition

used in questions when you are asking someone to pick one person or thing from a limited number of possibilities

Example

Which flavor do you want — chocolate or vanilla?

which + noun in a choice question

Jude asked the librarian which book the class should read first.

indirect question after asked

Common collocations

which one
which of
which way

Synonyms

what
Used when the set of possible answers is open, not limited — e.g., 'What book are you reading?' (any book), vs. 'Which book…?' (from a known set).

Grammar Patterns

which + noun + (modal) + verb

Usage Note

The answer is expected to come from a set of known options — unlike 'what', which is used when the options are open or unknown. Frequently used with 'of' (which of the…).

Common Mistakes

Which color you like?

Which color do you like?

In direct questions, the auxiliary verb (do/does/did) must follow 'which'.

What book do you want?' (when choosing between two specific books)

Which book do you want?

Use 'which' when the options are limited and known to both people.

2.determinerB1

Definition

used to make clear or ask about the exact identity of a particular person or thing among several

Example

Rin showed the new student which desk was hers.

show + which + noun + clause

The doctor asked the nurse which arm the patient had injured.

ask + which + noun in embedded question

Common collocations

know which
tell which
say which
decide which

Synonyms

which one
Used as a pronoun instead of a determiner — e.g., 'I know which one she picked' vs. 'I know which dress she picked.'

Grammar Patterns

know/say/see/remember + which + noun + clause

Usage Note

Common after verbs of knowing, showing, telling, and deciding. Unlike sense 1 (direct question), this sense often appears in statements or indirect questions where the speaker is identifying rather than asking.

Common Mistakes

She told me which is the best restaurant.' (when followed by a noun)

She told me which restaurant is the best.

When a noun follows directly, 'which' acts as a determiner before the noun.

3.determinerB2

Definition

used after a preposition to connect a clause that gives extra information about a time, event, or thing just mentioned in the previous clause

Example

The storm lasted all night, during which time the power went out twice.

during which time — formal relative determiner

Walid studied in Taiwan for three years, after which period he returned home.

after which period — linking time phrase

Common collocations

at which point
in which case
during which time
after which
by which time

Grammar Patterns

preposition + which + noun + clause

Usage Note

Frequently used in formal or written English. The preposition (during, after, before, by, in, on, at, for, as a result of) comes before 'which', and together they modify the noun that follows. In informal speech, this construction is often replaced with simpler structures.

Common Mistakes

He called at midnight, which time I was asleep.

He called at midnight, at which time I was asleep.

The preposition must come before 'which' in this formal pattern.

1.pronounA2

Definition

used in questions when you are asking someone to choose one or more people or things from a limited set, without repeating the noun

Example

Which of these jackets do you think would be warmer for a snowy day?

which + of + [group] expanded question

Asher has three cousins, but I cannot guess which is the eldest.

Common collocations

which of
which is
which are

Synonyms

what
'What' is used for open-ended choices — 'What do you want to eat?' (no limit) vs. 'Which do you want?' (from a limited menu).

Grammar Patterns

which + of + group noun / pronoun

Usage Note

Unlike the determiner sense (which + noun), this pronoun sense stands alone as the subject or object. It is almost always used with a limited set that is clear from context or introduced by 'of'.

Common Mistakes

Which of them you like?

Which of them do you like?

Auxiliary verbs (do/does/did) are required in direct questions with 'which'.

2.pronounB1

Definition

used as the subject or object of a relative clause to refer back to a thing, animal, or idea already mentioned, adding more information about it

Example

The movie, which Ramón had already seen twice, was still exciting.

noun + comma + which + non-restrictive clause

Linh's old bicycle, which she had owned since high school, finally broke down.

Common collocations

which is
which was
which has
which means

Synonyms

that
Can replace 'which' in restrictive clauses (no commas) — 'the book that I read' vs. 'the book which I read.' In non-restrictive clauses, 'that' is informal in British English and incorrect in American English.

Grammar Patterns

noun + which + relative clause

Usage Note

For people, 'who' or 'whom' is preferred over 'which'. 'That' can replace 'which' in restrictive (no comma) relative clauses, but not in non-restrictive (with comma) clauses. 'Which' refers to the immediately preceding noun, not to the whole clause — for clause reference, see the determiner relative sense.

Common Mistakes

The man which called you is here.

The man who called you is here.

Use 'who' (not 'which') for people.

My car, that broke down last week.

My car, which broke down last week.

'That' cannot begin a non-restrictive relative clause (with commas).

3.pronounB2

Definition

used in the pattern 'which is which' when talking about being able to see or explain the difference between two or more similar people or things

Example

The twins look so alike that nobody can tell which is which.

tell which is which — fixed idiom for distinguishing

The teacher mixed up the test papers and could not tell which was which anymore.

Common collocations

tell which is which
know which is which
which was which

Grammar Patterns

tell/know + which + is + which

Usage Note

The phrase 'which is which' is the most common form and is a fixed expression. The first 'which' refers to one set of items, the second 'which' to the other set. This sense is very common in everyday speech when items are nearly identical.

Common Mistakes

I can't tell which one is which one.

I can't tell which is which.

The second part does not repeat the noun; 'which' stands alone.

Idioms

which is which

idiom

Used when you cannot see the difference between two similar people or things.

The two puppies look exactly the same; I can't tell which is which.

Can you help me identify the real painting and the copy? I don't know which is which.

Word family

whichever
pronoun / determinerB2
whichsoever
pronoun / determinerC2

Synonym discussion

Sense: determiner/1

All three words can be used to ask about or refer to things, but they differ in how open the possibilities are. 'Which' presupposes a limited set of known options, often named or implied by context — e.g., 'Which film shall we watch?' (from a menu of available films). 'What' is used when the set of possible answers is open or unknown — 'What film are you watching?' (any film in existence). 'That' functions as a relative pronoun (not interrogative) in clauses that restrict meaning: 'the film that won the award.' A helpful test: if you can replace the word with a small set of options (this one or that one), choose 'which'; if the answer could be anything, choose 'what'; if you are defining or narrowing a noun, choose 'that.'

which ↗what ↗that ↗

Common collocations

Nouns

which way
which direction
which side

Phrases

which is which
which one
which of the two

Prepositions

which of

Etymology

Proto-GermanicOld EnglishMiddle EnglishEnglish

Which traces back to Old English 'hwilc', meaning 'of what kind or form.' This word was built from two parts: 'hw-' (the same root as 'who' and 'what') and '-lic' (meaning 'body, form, shape' — related to modern English 'like'). So its original sense was literally 'what-like' or 'having what form.' Over time, its meaning narrowed from asking about the quality or kind of something to asking for a specific choice from a defined group. The use as a relative pronoun (connecting clauses) developed in Middle English.

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which

which — determiner

1. used in questions when you are asking someone to pick one person or thing from a

Grammar Patterns

Usage Note

Common Mistakes

2. used to make clear or ask about the exact identity of a particular person or thi

Grammar Patterns

Usage Note

Common Mistakes

3. used after a preposition to connect a clause that gives extra information about

Grammar Patterns

Usage Note

Common Mistakes

which — pronoun

1. used in questions when you are asking someone to choose one or more people or th

Grammar Patterns

Usage Note

Common Mistakes

2. used as the subject or object of a relative clause to refer back to a thing, ani

Grammar Patterns

Usage Note

Common Mistakes

3. used in the pattern 'which is which' when talking about being able to see or exp

Grammar Patterns

Usage Note

Common Mistakes

which is which

which — adjective

1. any one that; no matter which one — used before a noun to say that the choice do

Grammar Patterns

Usage Note

Common Mistakes

Word family

Synonym discussion

Common collocations

Nouns

Phrases

Prepositions

Etymology

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