It is not enough to know that a thing works: you should also understand how and why it works. The rules of the road, for example, exist to keep people safe, but it is acceptable to break the rules under certain circumstances, such as when the only way to avoid getting flattened by an oncoming train is to run a red light. This is obvious, because drivers have a thorough understanding of the rules of the road and of their limits.

According to General Clausewitz, just like a good plan, theory is a guide to action. It accompanies you on the journey and helps to point the way. It helps to organize action. Creative-thinking expert Edward de Bono offered an example: "A two-finger typist with hundreds of hours of practice is still a two-finger typist. A few hours learning touch typing would have made a huge difference. It is the same with thinking."

But how do you evaluate a theory? Philosopher of science Larry Laudan explained that a theory should be evaluated by both the number of empirical problems it solves and how well it fits with existing theories. The theories of evolution and creationism can both explain the empirical problem of why men have nipples. But there is a glaring difference in how the two explanations fit with other theories. Evolution's explanation does not cause problems for the theory of evolution, because it fits seamlessly with other theories of biology and human development, which fit with theories of chemistry and physics, and so on. Human em¬bryos start out as females; only after several weeks does the Y chromosome kick in. With creationism, however, you should wonder: since man is created in God's image, why does God need nipples?