A good scientific theory is one which is falsifiable, which has not been falsified.

A good theory explains a lot but postulates little.

The theory of evolution by cumulative natural selection is the only theory we know of that is in principle capable of explaining the existence of organized complexity

A universe with a God would look quite different from a universe without one. A physics, a biology where there is a God is bound to look different. So the most basic claims of religion are scientific. Religion is a scientific theory.

Details that could throw doubt on your interpretation must be given, if you know them. You must do the best you can—if you know anything at all wrong, or possibly wrong—to explain it. If you make a theory, for example, and advertise it, or put it out, then you must also put down all the facts that disagree with it, as well as those that agree with it. There is also a more subtle problem. When you have put a lot of ideas together to make an elaborate theory, you want to make sure, when explaining what it fits, that those things it fits are not just the things that gave you the idea for the theory; but that the finished theory makes something else come out right, in addition.

[Evolution is] a theory in a special philosophical sense of science, but in terms of ordinary laymen's use of language, it's a fact, ... Evolution is a fact in the same sense that it's a fact that the Earth is round and not flat, [that] the Earth goes round the Sun. Both those are also theories, but they're theories that have never been disproved and never will be disproved.