Can someone give me clear rules when to use "what" and when "which" in case of sentences like " which/what "


"My access is arranged which/what saved a lot of time"

"Studies have shown that strawberries contains X which/what have alarmed scientists"

"I bought a car which/what will reduce my daily travel time."


  • 2
    These are all "which" sentences. "What" does not make sense here.
    – jlam55555
    Commented May 11, 2015 at 14:49
  • I give them as examples. I want to know when to use "what" and when to use "which"
    – robert
    Commented May 11, 2015 at 15:00

3 Answers 3


You're trying to use "which" and "what" as a pronoun, to refer to the subject that precedes it.

However, "what" as a pronoun can only be used for interrogative reasons, to ask for information (i.e. in questions such as, "What is he doing?").

"Which" would work here, because it is used to refer to a specified antecedent (i.e. the subject of the sentence, such as "my success," "studies," and "a car").

Look at the dictionary definitions for what and which for more information.

  • What and which are part of grammar; they don't have any meaning because they're pronouns, so dictionaries are the wrong place to look. Dictionaries are good for words with meanings, like etymology and entomology, but not for words that are part of the machinery of language. You need a grammar for that. Commented May 11, 2015 at 16:22
  • I agree with the answer provided, and I'd like to add that 'which' must be preceded by a comma since we are dealing with a non-defining relative clause.
    – saintjules
    Commented May 19, 2015 at 20:42

When "which" or "what" is used as a question, "which" is normally preferred when the options are limited, "what" is preferred when the options are unlimited.

For example:

What car do you prefer? (Unlimited options)
Which car do you prefer, the Volvo or the Mercedes? (Limited options)

What can indeed function as a relative pronoun in nominal relative clauses, e.g. sentences like "I took what they offered me." One way to think of it is a less formal synonym of that which. E.g. I eat what I like = I eat that which I like. These examples are from Quirk's grammar.

More examples: https://www.englishgrammar.org/relative-pronoun/

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