Simplicity (in scientific theories)

In evaluating which of several competing hypotheses is most plausible, scientists often use simplicity as a guide. This raises three questions: what makes one hypothesis simpler than another? Why should a difference in simplicity make a difference in what we believe? And how much weight should simplicity receive, compared with other considerations, in judging a hypothesis’ plausibility? These may be termed the descriptive, the normative, and the weighting problems, respectively. The aesthetic and pragmatic appeal of more simple theories is transparent; the puzzle is how simplicity can be a guide to truth.