When you have two competing theories that make exactly the same predictions, the simpler one is the better.

The explanation requiring the fewest assumptions is most likely to be correct.

Never increase, beyond what is necessary, the number of entities required to explain anything.

I consider that the chief dangers which confront the coming century will be religion without the Holy Ghost, Christianity without Christ, forgiveness without repentance, salvation without regeneration, politics without God, and heaven without hell.

The formal scientific definition of theory is quite different from the everyday meaning of the word. It refers to a comprehensive explanation of some aspect of nature that is supported by a vast body of evidence.

To be premature is to be perfect.