One of the most powerful tools used by sceptics is the principle of parsimony, often referred to as Ockham's Razor. This states, loosely, that when there are two competing explanations for something, the simpler should be preferred unless there is good reason to favour the more complex. It is this principle that means we don't conjure up aliens to explain crop circles when a combination of hoaxers and cider will do equally well. It is this principle that dissuades us from believing that Shakespeare was a myth created by the Victorians. And it is this principle, claim many atheists, that offers the best argument that God does not exist.
It is certain that Ockham's Razor is a valid and effective mental tool. If nothing else, we know this because much of science is based on parsimony, and science works. But I want to contend here that it is frequently misused, and is not as powerful as some people imagine.
The problem with Ockham's Razor is the illusion of certainty that it gives.
Imagine a black box. On the side is a switch, and on the top a light bulb. When the switch is pressed, the bulb lights; when it is released, the bulb is extinguished. But we cannot open the box to see its contents.
The simplest deduction about the contents of the box is that it contains a battery and some wire. Therefore this is the explanation we should favour. Other explanations are certainly possible: there might be an internal light-bulb and light photovoltaic cell to complete the circuit; or a clockwork mechanism rather than the battery; or a little pixie who ferries individual electrons around at lightening speed. But these explanations are discarded because they entail entities for which we have no direct evidence.
Yet Ockham's Razor does not actually prove that such things do not exist. We might draw the line at miniature pixies, but it is entirely possible that the box contains something more than a basic circuit; indeed, modern torches frequently contain diodes to ensure batteries can only be fitted in one way. Newton did not add a term to his theory of gravity about the colour of the objects in question - not because he tested and eliminated it, but because he had no evidence that colour had an effect, so he assumed it did not. But likewise, he did not include a term related to the speed of the objects compared to the speed of light. His reasoning was the same, yet we now know that on that point he was in error.
So the Razor can be suggestive, but it is not proof of anything; at best it is a presumption, and we should always be wary that it will frequently lead us into error. Which begs the question - if the Razor can lead us into error, and has no rational foundation (perhaps a subject for a post some other day), what use is it?
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