Main Difference: Many English learners often find the use of two interrogative pronouns what and which a bit tricky. The main difference between what and which is that what refers to an open set and which refers to a closed set. Let us analyze this difference further in this article.
What – Meaning and Usage
What is always used when we are referring to an open set. In simple terms, we use what when there are unlimited possibilities to the answer. For example, if I ask someone “What’s your name?” there can be millions of answers. Thus, we use what (not which) when we have no idea about the answer. What can be used as an interrogative pronoun, determiner and an adverb.
What is your favorite book?
What are you doing?
What is your first language?
What is the secret behind your success?
Which – Meaning and Usage
We use which if we are referring to a close set. That is, if there is a limited number of choices as the answer. For example, imagine that there are three books in your friend’s hand, and you want to know the best book out of them. Then you can ask, “Which book do you like the most?” Here, the answer will be one of the three books.
Which colour do you like the most – red, blue or yellow?
Which countries (out of these) have you visited?
Which hotel do you prefer, Savoy or Hilton?
Which can also be used before a pronoun or a noun with a determiner. What cannot be used in this manner.
Which of these necklaces do you prefer?
Which of you called me yesterday?
Which of the suspects murdered him?
Which can be used an interrogative pronoun, interrogative determiner and a relative pronoun.
Difference Between what and Which
What is used when we have unlimited possibilities as the answer.
Which is used when we have limited possibilities as the answer.
What is used as an interrogative pronoun, determiner and adverb.
Which is used as an interrogative pronoun, interrogative determiner, relative pronoun and a relative determiner.
What can not be used before a noun or pronoun before a determiner.
Which can be used before a noun or pronoun before a determiner.