What vs Which
What and which are two wh- words in English that can often be mistaken for each other. They both have many uses and meanings, and some of those meanings and uses largely overlap with only small differences. What can be used as a determiner, pronoun, and interjection. Which can be used as a determiner and pronoun.
As a determiner, what and which are often used almost the same way with slight differences. What is used as a question word used for a non-defined set of items while which often refers to predefined or implied sets of items. They can also be used as relative determiners in much the same way. See definitions for examples.
As a pronoun, in their interrogative forms, what is used for amount, type, and names, whereas which is used to determine specific items either mentioned explicitly or implied. What can also mean whatever and which can mean whichever.
As an interjection, what can be used to express surprise or to ask someone what they said or what they want, sometimes in a rude way.
Here are some definitions and examples to help make the use of these words clearer.
What (determiner)
1) A question word used for a non-defined set of items. Like which, but for non-specific things.
Examples:
What time will you go to the dentist tomorrow?
What drink is your favorite in the world?
2) Relative determiner. Used in place of the, that, or which. Can also mean whatever.
Examples:
He knows what choices he has.
I don’t care what plans you have made; you’re showing up to work or else!
3) Word used for emphasis.
Examples:
What a match! I can’t believe they won.
I went to the Great Wall last year. Wow! What beauty!
What (pronoun)
1) Interrogative word asking about the specification of a noun.
Examples:
What is the name of that old song?
I don’t know what they will do when they find out how much I spent on maple syrup.
2) Same as definition 2 for the determiner form but used without a noun.
Examples:
He knows what he must do.
I don’t care what you’ve got planned.
What (interjection)
1) Expresses surprise.
Examples:
What! You scared me! Where did you come from?
What! I can’t believe you said that.
2) Used to ask someone what they said or what they want. In the second case, it can be rude and used to express annoyance.
Examples:
What? I didn’t hear you.
What? I’m busy. Can’t you see that?
Which (determiner)
1) Used as a question word that functions like what when referring to either an explicit or implicit list of items.
Examples:
Do you know which route you’ll take?
Which musician has the best sound from the list?
2) Whichever.
Examples:
I don’t know which character you’re best at in this game but pick whoever you want.
You can choose which candy you like most.
3) Refers to an item that was mentioned before.
Examples:
I heard about the new law, which sadly prohibits me from cloning myself.
She invested in the new company, which lost her thousands in savings.
Which (pronoun)
1) Used as a question word that functions like what when referring to either an explicit or implicit list of items.
Examples:
Do you know which I should eat from this menu?
Which sounds the best?
2) Whichever
Examples:
Which you pick doesn’t matter. Just pick!
I’ll take which I can get.
3) Used as a relative pronoun to connect a dependent clause to an independent one.
Examples:
The keys which you left on the table are now in my hands.
His house which was built last year is already falling apart.
Main Points
- What and which are very similar words in many ways, but they have some differences.
- When used as an interrogative, which is used for specified sets of items or implied sets, whereas what is used for non-specified sets.
- What can be used as a determiner, pronoun, and interjection.
- Which can be used as a determiner and pronoun.