Ai Weiwei:

Double stool is a pair of stools connected and through its own logic, its own angle and the craftsmanship and being finely constructed by classic furniture makers. So those stools are Ming or Qing Dynasty stools that are a few hundred years old, very common at that time and have a perfect structure, three legs. 

And that time, of course, I'm very used to understand Marcel Duchamp’s ready made. But I still think I need to go one step ahead of it, so I needed to give a little bit more of my cultural background understanding. So the ready-made is no longer objects, but a cultural heritage. So I take China's culture or Chinese politics as a ready-made. So I restructure it and then make a commentary and very often it's kind of humorous and critical at the same time. So I developed this in more stools with no added elements and developed it into a self formed circle and it's very strong structurally and again, no nails. It takes a profound knowledge about furniture making and only Chinese can do that.