(I will be away on travel this week so will be reposting an old series, edited and updated, that discusses the nature of science and the difference between science and religion. New posts start again on Monday, April 21, 2008.)

A few days ago I was working in my backyard when I noticed that the outdoor thermometer that I had fixed to a fence had disappeared. The mountings were still there but had been pulled away slightly. I thought that maybe the wind had blown it off and so I looked at the ground underneath but the thermometer was not there. There is a bed of pachysandra nearby and I looked nearby in it but no luck. I was baffled.

I pondered the various options for explaining the missing thermometer. One was that the wind had been strong enough to rip the thermometer from its mounting and blow it farther away into the pachysandra. The other was that it had fallen to the ground below and had then been taken away by squirrels or the neighbor’s cat. The third was that neighborhood children had borrowed it without permission for some experiment. The fourth was that the International Outdoor Thermometer Cartel (IOTC) had raised the price of these thermometers to such a high value that organized crime gangs were stealing them and selling them on the black market. The fifth option was that aliens had taken it away as a souvenir of their clandestine visit to Earth.

Given these options, I decided that #1 was the most likely one and looked in the pachysandra over a larger area and, sure enough, I found it.

The reason for this anecdote is that it illustrates that I used something that we all use all the time (whether we are consciously aware of it or not), and that is Ockham’s razor to make choices among competing theories.

According to the Encyclopedia Brittanica, the principle behind Ockham’s razor (also called the law of economy or the law of parsimony) was stated by the scholastic William of Ockham (1285–1347), as “Plurality should not be posited without necessity.” The principle is also expressed as “Entities are not to be multiplied beyond necessity.” Ockham did not himself use the word ‘razor’, that was added to his name later by others.

The principle gives precedence to simplicity, but there are two ways it can be used. In the first case (which is more closely aligned with Ockham’s intent), it says that you should not postulate more elements for anything other than the minimum required. For example, in the case of my missing thermometer, if I postulated one theory that a cat had taken it and a competing theory was that a cat that had a striped tail and a scar on its forehead had taken it, then in the absence of any extra information, the former theory is to be preferred. The latter theory just adds elements that do not add any necessary information to the explanation. The application of this version of the principle is fairly straightforward. One seeks the smallest subset of elements of a theory that provides an adequate explanation of whatever you are trying to explain.

The more problematic (but common) use of Ockham’s razor is when you try and apply it to a situation where there are two competing theories that share either no common elements or there exist at least some necessary elements of one theory that the other does not possess. We commonly interpret Ockham’s razor in those situations as requiring us to choose the simpler of the two theories. But simplicity may well lie in the eye of the beholder and it may not be easy to get agreement.

So, for example, in the case of the thermometer that was found some distance away from its mountings, the simpler explanation (for me at least) was that of the wind. If called upon, I could cite Bernoulli’s Principle and the laws of motion to support my preference. That explanation is enough to satisfy me.

But this may not be true for someone else. For someone who is a believer in the existence UFOs and space aliens, a theory that alien vandals landed in my garden, tore the thermometer from its moorings, threw it away in the pachysandra and left in their spaceship, might be the “simpler” explanation. After all, it does not involve the use of calculus.

That is exactly the problem in many of the science and religion discussions. Apart from those people who reject science altogether, the integration of science and religion into one coherent philosophical framework becomes one of the most difficult challenges and there is no simple solution to it. And all of us use Ockham’s razor to resolve it, even though the results are not the same for everyone.

A belief in the existence of god implies that there must be at least some phenomena caused by the intervention of god that lie outside the purview of science. (I am not considering the point of view that god created the world and its laws in one instant of time long ago and then has had a completely hands-off policy since then.)

For example, Biblical literalists will start with the assumption that the Bible is a historical document and that the events described in it (the world was created in six days and is only 6,000 years old, Joshua caused the Sun to stand still, Noah’s flood did occur, etc.) all actually occurred. They will then painstakingly and tortuously try and reinterpret all evidence to be consistent with these axioms. The website Answers in Genesis goes to extraordinary lengths to try and answer questions such as “Where did Cain find his wife?” and “Did dinosaurs live alongside humans?” These are questions that do not trouble anyone who does not treat the Bible as an authoritative source for science and history.

But even those who take the Bible less literally have to confront difficult questions because at some point, the question is going to arise about where you draw the line and ascribe something to the actions of god. Each person will draw the line between god’s actions and the actions of natural laws differently, depending on their personal level of comfort with the explanation.

This is something that believers in any theistic religion have to confront. Some will believe that any event that does not have a ready explanation to hand (a death in the family, an escape from injury, an unexpected recovery from a serious illness) are directly due to god’s intervention to change the course of events. In order to deal with the existence of evil in the presence of an omnipotent and loving god, believers usually end up having to postulate that god’s actions are inscrutable and that we cannot know the answers to at least some of the events that occur in the world.

At the other end, others might believe that god does not actually cause a change in the natural sequence of events but instead exerts his/her influence by working through people. In other words, people are the agents of god’s actions and the sole mechanism by which he/she influences events. So people are cured of illnesses because god inspires researchers and physicians, and so on.

There are also an infinite number of intermediate states between those two extremes. For example, people like the biochemist Michael Behe, who is an intelligent design advocate and author of the book Darwin’s Black Box, accept natural explanations for everything except for a few selected phenomena at the biochemical level (such as the blood clotting mechanism or the creation of the bacterial flagellum) that he feels are unlikely to have been created by natural processes. (See the New Yorker article by H. Allen Orr for a clear description of what Behe’s argument is. Cory also sent me a link to a nice article written by John Rennie, editor of Scientific American, that addresses some of the key points raised by ID advocates.)

Or one can use decide that there is no god (or supernatural entity of any kind), and all that exists is the material world. This is the position of philosophical naturalism or atheism. (I am treating the two terms as effectively synonymous, although professional philosophers might disagree).

So we are left with only Ockham’s razor with which to make a decision but in this case, it is a very personal razor whose use will satisfy only us. I personally find that assuming no god exists makes everything simpler and much more meaningful.

But those who are committed to believing in the existence of god despite the lack of evidence for his/her existence will not agree with me that this is the simplest explanation. They will likely say that having an inscrutable god who for some reason allows unspeakable cruelties is a ‘simpler’ way of understanding the world.

Which position one ends up taking is thus largely determined by deciding which is ‘simpler’ to believe in, which usually means deciding which belief structure you want to believe in and find personally enriching and meaningful, since there is no unambiguous measure of simplicity for incommensurable theories.