Parsimonious
What if more than one theory resists falsification? How do we choose—or do we? A fourteenth century Franciscan monk, William of Occam, or Doctor Invincibilis as he was nicknamed for his skill in debate, provided the answer: “The simplest theory that completely explains the facts is best,10 which we now know as “Occam’s Razor.” This may not seem like much, but when the Copernicus proposed the heliocentric system, it was the deciding factor in preferring it to Ptolemy’s geocentric system.
Both were about equal in their ability to predict phenomena such as solar and lunar eclipses and the variable brightness of planets. The Copernican system raised questions nobody could answer at the time such as why things did not fly off a moving earth and it required the complicated double motion of a revolving and rotating earth. However, it eliminated the incredibly complex Ptolemaic system with its still proliferating array of forward and retrograde motion along orbits supplemented with epicycles and eccentrics—that is, additional orbits either centered on or tangential to the main orbits and to one another—unique to each star and planet. Furthermore, Indian, Arab, and European astronomers all had different versions of the Ptolemaic system. The Catholic Church initially agreed with Copernicus, leading to the Gregorian calendar that we still use. It was only later as the theological implications began to sink in that the Church tried to unseat the Copernican universe.“Parsimonious” does not necessarily mean “easy to understand.” Rather, it refers to the number of components and their relationships. A theory based on difficult mathematics but using a single formula explaining how to combine operationally defined, accurately measured variables is parsimonious. A theory of limited application couched in jargon with elaborate qualifications is not.