OK, but it’s not too hard to describe what makes a thing blue. The only obvious sticking point is who’s standard of blueness we’re using. Perhaps a “blueness function” would be better than an equivalence class of all things blue, then. Regardless, determining whether or not a given thing is blue doesn’t seem to be what the OP is asking about; I’m suggesting that this suffices.
I think you’re missing the point of the post. The problem is about blue qualia, not the category blue. There would still be blue in a world of p-zombies, but not blue qualia.
Can’t we just define “blue” or “blueness” or what have you to be an equivalence class and be done with it?
Well we wouldn’t want to “just define” a word that’s supposed to refer to something in the world, without figuring out what that thing is yet.
OK, but it’s not too hard to describe what makes a thing blue. The only obvious sticking point is who’s standard of blueness we’re using. Perhaps a “blueness function” would be better than an equivalence class of all things blue, then. Regardless, determining whether or not a given thing is blue doesn’t seem to be what the OP is asking about; I’m suggesting that this suffices.
I think you’re missing the point of the post. The problem is about blue qualia, not the category blue. There would still be blue in a world of p-zombies, but not blue qualia.