Deciding between explanations

We can see from what we learned in the last step how extraordinary and supernatural beliefs might arise and be held with great conviction. If any belief can be made to fit the evidence, then those who hold such extraordinary beliefs can often explain away what may appear to be inconsistencies. How, then, if any belief can be made consistent with the evidence, can we decide which is the most likely to be true?

Ockham’s Razor

The philosopher and theologian William of Ockham (1285-1349) pointed out that, where one is presented with two hypotheses that are otherwise equally well-supported by the available evidence, you should always pick the simplest hypothesis. In particular, we shouldn’t gratuitously introduce any superfluous entities. This principle, known as Ockham’s razor, is very sensible. Take, for example, these two hypotheses:

  1. There are invisible, intangible and immaterial fairies at the bottom of the garden, in addition to the compost heap, flowers, trees, shrubs, and so on.

  2. There are no fairies at the bottom of the garden, just the compost heap, flowers, trees, shrubs, and so on.

Everything I have observed fits both hypotheses equally well. After all, if the fairies at the bottom of my garden are invisible, intangible and immaterial, then I shouldn’t expect to observe any evidence of their presence, should I? Does the fact that the available evidence fits both hypotheses equally well mean that I suspend judgement on whether or not there are fairies at the bottom of the garden?

Of course not. The rational thing to believe is that there are no fairies, for that’s the simplest hypothesis. Why introduce the unnecessary fairies?

Extraordinary claims

When it comes to assessing extraordinary claims a humanist will often, then, ask which hypothesis is the most economical. The simplest explanation is not necessarily the correct one, but it is often the rational starting point.

We should not assume that extraordinary claims are false, but we should be sceptical. We should also take into account the regularity with which such claims are made, and the history of how unreliable they often turn out to be.

‘When anyone tells me, that he saw a dead man restored to life, I immediately consider with myself, whether it be more probable, that this person should either deceive or be deceived, or that the fact… should really have happened.’

David Hume, An Enquiry Concerning Human Understanding

The philosopher David Hume was sceptical when it came to claims about miracles. He believed we should always ask whether it is more likely that the normally secure laws of nature broke down for a moment or that something else less exciting happened. Perhaps, for example, we were mistaken about what we saw or heard (we can be more susceptible to error when it is something we want to believe). Or perhaps someone is lying to us, possibly with an ulterior motivation. Lying, forgetting, and illusions can sometimes seem unlikely, but we know they do actually happen – we have lots of evidence of them happening. Hume would say they are more likely to have occurred than that the laws of nature broke down, and so it is rational to conclude that, instead, we were mistaken or are being deceived. Hume’s logic applies just as much today to claims of faith healing, alternative medicines, and sightings of UFOs. We should always ask whether our desire to believe something is true might be influencing our rational judgement.

Question: What is the best approach to take when we hear an extraordinary claim?

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This article is from the free online course:

Introducing Humanism: Non-religious Approaches to Life

Humanists UK