Sharpen Your Genealogy with Ockham’s Razor

William of Ockham was a Franciscan friar who lived at the turn of the 14th century. A celibate who lived that long ago is not the most likely of topics for a genealogy article. He is my subject for today not because of who he begat but because of what he wrote. Perhaps his most oft-quoted line is, “Pluralitas non est ponenda sine neccesitate,” which translates to “plurality should not be posited without necessity.” That translation might not clear things up all that well, nor is there much help from the apparently shaving related name the statement usually goes by, “Ockham’s razor.” A little thought, however, turns it into a powerful tool for judging possible explanations for your data.

Ockham’s razor is now generally stated along these lines, “if you have more than one way that your facts can be explained, the simplest way is probably the closest to the truth.” Notice that this isn’t a rule of logic; it’s a guideline. You can’t definitively win or lose many arguments based on Ockham’s razor, you can’t prove a hypothesis, but you can increase your chances of being right by paying attention to Ockham.

As you comb through your data, you may come up with several interpretations that explain what you have found. Since the hypotheses all explain what you know, how do you chose which one to pursue? Many people chose the most exciting possibility, the one they hope is true, the one they want to believe no matter what. They might even assume that it is true and leave it at that. Ockham’s razor will probably tell you to concentrate on a different explanation, the one that “posits” the least “plurality”—the one that makes the fewest assumptions, and requires the fewest coincidences. It will be the simplest and easiest to deal with and the most likely to be true.

Assumptions are, by definition, possibly false. String together a large enough number of assumptions and you will end up with a result that is almost certainly false. It only takes one wrong assumption to throw off an entire argument. The fewer the assumptions, the less convoluted the argument, the better chance you have of being correct and pursuing new information in the right place, new documents in the correct county at the right time, for example.

Thinking about Ockham’s razor has another benefit. It forces you to think about your assumptions. Many of the assumptions in a hypothesis are hidden. That is, they aren’t explicitly made. One of the most common hidden assumptions is that records from the same area that contain the same name are referring to the same person. Often they are not. Thinking about your assumptions and figuring out how likely they are to be true moves a logical argument forward. If you prove an assumption to be wrong then follow Ockham’s razor to the simplest hypothesis that fits the new data and continue.

Ockham’s razor doesn’t imply that the unlikely never turns out to be correct, only that a complex string of convoluted events is not the first thing to concentrate one’s efforts upon. It may, however, be the only hypothesis that works. My ancestor Isaac Evans lies buried between his two wives. The first was named Phebe and came from a town hundreds of miles away from where Isaac lived at the time of their marriage. On the other side is his second wife, Phebe, who came from the same exact town hundreds of miles away where she was still living when they married. Before those graves were found, I had several hypotheses. That Isaac had two wives with the same name, who came from the same distant town, wasn’t the first hypothesis to test but it was the last hypothesis left standing.