Well, it’s hard for me to describe well but it’s something like this.
You have a Category with Members in that Category.
But the Members are not identical: You can’t replace one with another. But they belong in that category.
However, as you get further and further away from the Category, each Member gets less and less like the Category and more like “Something Else”.
It’s only when a threshold of some kind is passed, probably a large gap of “nothing” does the “Somebody Else” assert itself and start a new Category.
I’m representing it here with numbers. I don’t know if its is the best way to illustrate this.
So, it is a sorted list.
and actually, numbers are not a good way to illustrate because the last member of the category does NOT belong in the next category, no matter how you cut the categories. But it is also furthest away from its own Category and closest to the next while also not belong to the next category.