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Which is the correct usage?

  1. What is the best book for learning English grammar?
  2. Which is the best book for learning English grammar?

Also, can you give other examples where we could use either?

2

I remember a rule (roughly defined though)! 'what' defines, and 'which' selects.

So, ask yourself. Are you asking in general? If yes, use 'what'. If you have certain books that you and a person whom you are asking both know, use 'which'. Take simpler example -"What food do you like?" is a general question. "Which food do you like?" makes you think that you have a choice or some option - Chinese or Mexican?

'what' to talk about any general book (defines), and 'which' to select (choose from a set of books both of you understand).

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3

It depends. You would use 1. for books in general, without having specific books in mind. You would use 2. for example if you have two books in front of you - in that case, 'which' would really indicate 'which of these two books'.

Ironically, you are almost giving another example yourself:

Which (of the following sentences) is correct?

What is the correct usage?

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