How Does Quine's objections to modal logic 3 - extensionality and intensionality Work?

Quine says that modal logic doesn’t always work because it plays fast and loose with what things really are, extensionality vs. intensionality.

Think of a toy box full of blocks. If you’re only looking at the shapes and sizes, like how many sides each block has or how big they are, that’s like extensionality, you're just focused on what things are, not why they are that way.

But if you start thinking about what makes a block special, maybe it's red, or it came from a special bag of blocks, that’s intensionality. You’re now looking at the story behind the block, not just its size and shape.

Quine says that in modal logic, we sometimes mix these two worlds: we treat things as if they're only about their shapes (extensional), but then we talk about how they could have been different, like if a red block might have been blue (intensional). That’s confusing, it's like saying the same toy box can be both a box of blocks and a magic bag that changes its contents every day.

So Quine says: “Let’s stick with one world at a time.” If we want to talk about what things could be, let’s make sure we know why they are what they are, not just what they look like.