Ockham's Razor Cuts Both Ways: The Uses and Abuses of Simplicity in Scientific Theories

Article excerpt

IN CARL SAGAN'S NOVEL CONTACT, heroine Ellie Arroway manages to travel through wormholes into uncharted regions of the universe, rendezvous with intelligent extraterrestrial life, and return safely to earth to tell her colleagues about her amazing journey. (1) There's only one problem: no one believes her. Ellie's entire adventure occurred within a span of a few moments, and observers did not even see her spacecraft leave its launch site. Unable to document her reported experiences, Ellie's colleagues conclude that there is simply no compelling evidence that her adventure actually happened.

Of course, as readers of the novel, we know that Ellie is right and her colleagues are wrong. Why then don't they believe her? They doubt her story because, as good scientists, Ellie's peers examine all hypotheses using the honored principle of Ockham's Razor. That is, with all other things being equal, "the simplest hypothesis is most likely to be correct." They scrutinize Ellie's elaborate claim, involving mind-boggling excursions far beyond the range of established science, and find the story to be fantastically improbable. Even Ellie must admit that the finely honed blade of Ockham's Razor seems to slice her tale to pieces.

Although Ellie and her plight are fictitious, her harrowing brush with Ockham's Razor raises interesting questions for skeptics. Like Ellie's scientific colleagues, we have learned to accept Ockham's Razor as a powerful tool for weeding out bogus theories. But how do we know that the maxim "simpler is better" will always lead us down the royal road to truth? How can we say, prior to further investigations, that simple theories are automatically more likely to be true than complex theories? Might not Ockham's Razor, thought by many skeptics to be the surest weapon against pseudoscience, simply be an unproven philosophical assumption? If so, perhaps we will share the fate of Ellie's peers and reject the correct answers simply because they don't conform to prior expectations.

This article presents a brief historical sketch of the principle, and cites examples of the misuse of Ockham's Razor to support dubious theories and how that misuse led to the rejection of good science. This discussion leads to an attempt to identify the limitations and qualifications needed to apply the principle properly when choosing among various theories. I then try to determine what justification, if any, we can have for using Ockham's Razor, and argue that skeptics should learn to use the principle carefully in conjunction with other criteria of theory selection. I hope to show that Ockham's Razor is a dangerous weapon if mishandled, but that those who follow the proper safety precautions will find it to be a very helpful tool for evaluating theories.

The History of Ockham's Razor

The principle of Ockham's Razor is named after William of Ockham (1285-1349), a distinguished medieval philosopher and theologian. Contrary to popular assumptions, Ockham did not invent the principle that has become associated with him. The idea that simplicity and efficiency are important advantages of a theory dates back at least to Aristotle, who stated that "the more perfect a nature is, the fewer means it requires for its operation." (2) Centuries after Ockham's time, Isaac Newton would also cite the principle of simplicity in his Principia Mathematica: "We are to admit no more causes of natural things than such as are both true and sufficient to explain their appearances." (3)

Ockham emphasized the principle of parsimony as an antidote to the various unwarranted assumptions he perceived in the philosophy of his time. He used a number of different formulations of the principle in his writings. He stated, for example, that "it is futile to do with more what can be done with fewer," and perhaps most famously, that "plurality should not be assumed without necessity." (4) A common term for this concept is parsimony. …