Francis Bacon on root of superstition

Tuesday, January 12, 2010
(If you spot any errors (in my maths, for example) let me know)

Francis Bacon (1561-1626)

The general root of superstition is that men observe when things hit, and not when they miss; and commit to memory the one, and forget and pass over the other.

Bacon is a pivotal figure in the development of the modern scientific method. Here he puts his finger on a common error, an example of selection bias.

Consider these anecdotes:

“Joan was thinking about Mary, whom she only thinks about rarely, and whom she had not heard from for a year. Later that same day, Joan’s phone rang, and it was Mary! Joan is clearly psychic!”

“It looked as if John would die, but I prayed he would get better, and he did. God answered my prayer!”

Such anecdotes can appear to provide compelling evidence of psychic abilities and supernatural events, particularly when many are collected together in a book or article. But do they supply good evidence of such supernatural phenomena?

Let’s focus on the first anecdote for a moment. Let’s focus on the first anecdote for a moment.

Suppose each of us knows five people we think about rarely – only five times a year, say - and from whom we hear only, say, once a year. Suppose each of us also knows 10 people very well. These aren’t implausible averages, I’d suggest. And they entail that, on average, within roughly any 7 and a bit year period, one such coincidence will happen to one person you know very well, and to ten of the people whom you know very well know very well.

Because such coincidences are dramatic, they make memorable stories. It is hardly surprising, then, that we should hear such stories told and retold even by people whom we know very well and whom we have every reason to suppose are being accurate and honest. But then the fact you have heard a handful of such stories does not provide you with any evidence of psychic powers.

Our mistake is to focus on the few “hits”, the coincidences, and forget about the many “misses” – all those occasions on which people thought about someone they rarely think about whom they haven’t heard from in years, who didn’t then immediately get in touch with them.

We should be similarly wary about the second anecdote. Given the huge numbers of sick people prayed for daily, it’s hardly surprising if a few make astonishing recoveries. We should expect this by chance. If we ignore the “misses” – all those occasions on which sick people were prayed for but they experienced no astonishing recovery, and focus only on the “hits”, the small proportion of occasions the person recovered, we can, again, easily convince ourselves that that we have evidence of the miraculous efficacy of prayer.

Of course, none of this proves that people don’t have psychic powers, or that miracles don’t happen. But it does explain away much of the evidence on which people base their belief in such phenomena.