Beauty criterion (Dirac) - The idea that more aesthetically pleasing a theory is the superior it is. In nature this criterion does not stand up to the actual test -- whether or not forecasts of a given theory agree with observational tests -- however considering that it is a wholly aesthetic quality which is being tested, a lot of the most successful theories (that is, special relativity, general relativity, quantum electrodynamics, and so forth) match the condition particularly fine.