Some native speakers use what and some which in the following examples:

  1. Which/what color is this?
  2. Which/what is your favourite book?(without giving any options)
  3. In which/what school do you study?

In my opinion, which is used when we give options to the listener. Isn't it?


Which color is this?

There's a list of colors, or only so many possible colors. You only want one of those colors in the list/that is possible.

You might not be aware of the list/which are possible, so if someone asks you this unexpectedly, it's OK for you ask "What possible colors are there?"

What color is this?

There's no list, so you're not expecting the reply to conform to anything.

You also can ask this if you don't know the name of a color at all.

Even if you don't know the name, but there's only so many possible colors (e.g. you're asking the color of 1 specific crayon out of set of 64), you might still use which.


Yes, which generally indicates a selection from separate options. They may be given or implied, perhaps by context. In many cases whee the options are separate, but very many options exist, the two have more or less identical meanings. Consider:

Which author do you like best?

If there is no context to narrow the possible choices, then the options are "eveery author the person addressed knows of" and the meaning is the same as

What author do you like best?

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