Grammar question: which vs. what

Which of the following two questions is grammatically correct?

  1. “Which parts are actively being worked on?”

  2. “What parts are actively being worked on?”

[sub]Never mind you about the preposition on the end. :stuck_out_tongue: [/sub]

Both of them sound OK to me but they both seem kinda wrong, ya know? Like they don’t smell right.

Both are grammatically correct, though I would tend to go with #1. “What” and “which” are closely related (and are sometimes used interchangably), but I see them as slightly different in meaning. Asking “which?” indicates a choice from a specific set of options, whereas asking “what?” is more open-ended. The sense I get from #1 is: “This car has 10 parts that need to be fixed. Which parts are actively being worked on?” #2 gives me the impression that the parts haven’t previously been identified: “I see your car is in the shop. What parts are actively being worked on?”

The reason I would tend to go with #1 is that the word “parts” implies that you are choosing from a predetermined list. Even in my example, the parts are limited by the “your car”. I couldn’t think of a good example using “parts” where I would pick “what” over “which”.

Here’s an example that is clearer as to the distinction:

  1. “I like egg shell white or meringue white for the dining room. Which color do you like?”

  2. “I don’t care what we paint the dining room. What color do you like?”