I think the default way people tell a stool from a table is that a stool is something on which you sit and a table is something on which you don’t sit but put stuff.
It’s not about whether the surface is flat or the amount of legs. You seem to argue that the identity should be defined about such “natural” or objective qualities without really making a case for it.
Your concept of a table is not the one that’s used by most people. Most people don’t have a problem imagining a 5-legged table and call an item like http://www.ikea.com/us/en/catalog/products/10135659/ a stool instead of a table.
It’s just an example.
I think the default way people tell a stool from a table is that a stool is something on which you sit and a table is something on which you don’t sit but put stuff.
It’s not about whether the surface is flat or the amount of legs. You seem to argue that the identity should be defined about such “natural” or objective qualities without really making a case for it.