A Close Shave with Realism: How Ockham's Razor Helps Us Find The Truth

Many distinct theories are compatible with current experience. Scientific realists recommend that we choose the simplest. Anti-realists object that such appeals to “Ockham’s razor” cannot be truth-conducive, since they lead us astray in complex worlds. I argue, on behalf of the realist, that always preferring the simplest theory compatible with experience is necessary for efficient convergence to the truth in the long run, even though it may point in the wrong direction in the short run. Efficiency is a matter of minimizing errors or retractions prior to convergence to the truth. 0.1 Realism and Ockham’s Razor There are infinitely many, incompatible theories consistent with any finite amount of experience, so how can we choose among them? The answer is easy: apply “Ockham’s razor”. In choosing a scientific hypothesis in light of evidential data, we must frequently add to the data some methodological principle of simplicity in order to select out as “preferred’ one of the many different possible hypotheses, all compatible with the specified data (Sklar 1977; p. 100). Why be guided by simplicity? Scientific realists would like to say something like this. . . . [A]mong the . . . theories consistent with our observational data, some are better explanations than others in virtue of their greater simplicity or elegance or unifying power and . . . these virtues are indications that those theories are true (Papineau 1997; p. 9, my emphasis). Great! But there’s a catch. . . . [T]he connection between simplicity and truth seems so dubious. ...[I]f no argument can establish such a connection, what reasons do we have in the first place for invoking simplicity in our mechanism for choosing (Sklar 1977; p. 132)? Indeed, how could there be such a connection? A fixed bias toward simplicity (or toward anything else) can no more indicate truth than a broken thermometer can indicate temperature. An indicator has to be sensitive to what it indicates, but Ockham’s razor favors simplicity no matter what. At least the errors incurred by Ockham’s razor are corrected, eventually, by future experience. It is this feature that makes the rule, “Adopt the simplest hypothesis compatible with the present data,” seem more innocuous than might first appear. For even if we do make this choice, we are not stuck with it, in the sense that ongoing experimentation can “test” our choice and, conceivably, reject it in favor of some more complex hypothesis (Sklar 1977; pp. 132-33). But that doesn’t explain much, since a mistaken presumption that the world is complex would also be corrected, eventually, by future experience. Nor does it help to stack the deck in favor of simplicity in advance. All we have to say is that the simpler laws have the greater prior probabilities (Jeffreys 1985; p. 47).1 There can be a prior bias toward simple worlds even when there is no prior bias toward simple theories. Suppose there are two theories, a “Ptolemaic” one with lots of free parameters and a “Copernican” theory with none. We are urged to “keep the door open” to the simple theory by assigning it a real-valued probability greater than zero (perhaps far less than the prior probability of the complex