I like to ask my students this: What is clay?
Often they are puzzled. Mud or dirt is their usual response. I like to explain that clay is drawn from a long process of erosion that occurs over thousands of years. I tell them that clay started as mountains of rock which were battered by glaciers, windstorms, and rain turning them into boulders, rocks, sand and finally clay. The clay is host to colonies of bacteria and organic decay that make the clay flexible and give it plasticity. Once the children learn this I hope that they gain a new understanding of what clay is. Some get it others don't.
Clay is also much more--in a philosophical sense. Clay is earth. It is substance. It can be liquified and poured into molds to mimic any object. It can be subtracted, added, divided and multiplied. It can withstand extreme cold(vitrified) and intense heat. It can be extremely strong(see Space Shuttle) or extremely fragile. Clay can heal (http://www.sciencedaily.com/releases/2008/04/080406155621.htm) infections. It can calm nerves, help with arthritis, and exfoliate dry skin. It can be used to hold things, transport, and store. It can insulate. It can house people. It can be eaten.