cleve callison’s blog

I was reading an article about Occam’s Razor (and how’s that for an attention-grabber, sports fans) that defined it along the lines of “Of two possible explanations for something, the simplest one is probably correct.” That’s been bothering me ever since. It rather seriously mis-states what Occam’s Razor is all about. It has nothing to do with probability and is not a predictor.

The logical principle elucidated by the Franciscan friar William of Occam (or Ockham), c. 1285-1349, is sometimes given as Numquam ponenda est pluralitas sine necessitate. “Entities are no to be feigned without necessity” is one translation. Let’s say we had theory A (simple) and theory B (complex). If we relied just on the formulation above and new evidence came to light that theory A can’t explain, then wouldn’t that prove Occam’s Razor (OR) wrong?

Not at all. In fact OR demands that the simpler explanation that accounts for all the observed phenomena is to be accepted as correct. It can’t be proved or disproved; it’s an axiom or heuristic principle. We don’t say that in Euclidean space “parellel lines probably never meet.” By definition, they can’t.

For much of the Middle Ages the Ptolemaic system was capable of explaining the motion of the stars and planets. It was based on the notion that they had to move in circles (because, as we know from Aristotle, circles are the perfect shape). To explain observed irregularities astronomers had to add circles on top of circles (epicycles) in ever more complex patterns.

Now, of course, we “know” that the movement of Earth around the sun (Copernicus) and the elliptical nature of planetary orbits (Kepler) explain the  motions we see. But how do we know that we know this? In theory epicycles could multiply and be refined endlessly to account for new observations; but eventually OR caused that monstrously complex system to collapse under its own weight.

Here’s the ironic part: probably many today would use OR to argue against the idea of a supernatural Creator. But for Occam himself, his principle was a grand demonstration of God, the one entity who exists by necessity and whose marvelous economy is to be found throughout the plenitude of created world.