It's the impetus behind the question "Is a hotdog a sandwich?" What does it mean to be a sandwich? What are the properties of sandwichness? When does something stop being a sandwich?

What's the line between pasta and bread? Bread and cake? Shoe and slipper? The fact that all fruits are vegetables, but not all vegetables are fruits, but it turns out most of them are, in fact, fruits, and half our fruits are actually nuts or some shit.

So to put an exemption on a "slipper", you have to rigidly define what a slipper is. Because "yeah, that's a slipper" doesn't pass muster. Because you and I can disagree on what a slipper is. On where the line between slipper and shoe is. But if we legally define a slipper as any article of clothing designed to be worn on the foot with a felted or cloth sole. Boom, we have something we can agree on. As long as the item meets all of the legal qualifications, it's legally a slipper. And we can fuck subjectivity right out the window.

But of course, where there are rules, there are games. And the goal of the game is to get as much as possible while giving up as little as possible.