A category is supposed to be a container: things are in it or out, and the argument is about the things. The foundation says a category is a point on a circle, and a point has no inside. Nothing is in a category; membership is a mark a reader made about how far a thing stood from a named condition, and the thing did not move — which is why Pluto could leave the planets unchanged, why one tomato can be a fruit and a vegetable in a single ruling, and why no list of what a chair is closes. … readWhat Is a Category