Qualitative Process Theory
Things move, collide, flow, bend, heat up, cool down, stretch, break and boil. These and other things that happen to cause changes in objects over time are intuitively characterized as processes. To understand common sense physical reasoning and make machines that interact significantly with the physical world we must understand the qualitative reasoning about processes, their effects, and their limits. Qualitative Process theory defines a simple notion of physical process that appears quite useful as a language in which to write physical theories. Reasoning about processes also motivates a new qualitative representation for quantity, the Quantity Space. This paper includes the basic definitions of Qualitative Process theory, describes several different kinds of reasoning that can be performed with them, and discusses its implications for causal reasoning. The use of the theory is illustrated by several examples, including figuring out that a boiler can blow up, that an oscillator with friction will eventually stop, and how to say that you can pull with a string, but not push with it.