The nature of experience and evidence

You hear a crash and a bang late at night, perhaps it wakes you, what could it be?

We've all experienced surprise like this, and perhaps even fear, especially when confronted by sensual stimulus (like noise or feelings) that can't necessarily be seen directly. A frantic thought process ensues as we scramble to identify possible causes, we all seek causes for things its in our nature; from an evolutionary perspective it's obvious to understand why establishing potential causality would be useful from a survival point of view, without it our bodies would be totally unprepared for whatever happened next.

Did something fall, is someone breaking in, is there a ghost? We can't disprove any of these ideas without evidence but a lack of evidence leaves us with only statistics to go on, what's more likely? That a decrease in ambient temperature caused the central heating pipes to contract and make a noise, or, that every known physical law of nature has been temporarily suspended and a phantom from beyond the grave has taken time out from a busy haunting schedule to bump into the kitchen table (how ethereal beings interact with real molecules is perhaps a philosophical point for another time)?

Evidence is the raw material that we use to help us sort out the useful ideas from the frivolous ones, in the mysterious case of what went bump in the night, how about a pigeon flying into the bedroom window? Pretty unlikely you may think, but how much more likely than a poltergeist, 100 times, 1000 times or more? A quick inspection of the windows may even turn up a greasy imprint like the one in the picture, sealing the deal, not 100% of course (an angel might have put it there to fool you) but good enough for me to settle back down to sleep, case closed.

None of this commentary on Human nature is new of course, back in 1748 a rather smart Scottish philosopher called David Hume wrote a book that explored such ideas, here is a short extract.

An Enquiry Concerning Human Understanding 1748 - A miracle is a violation of the laws of nature; and as a firm and unalterable experience has established these laws, the proof against a miracle, from the very nature of the fact, is as entire as any argument from experience can possibly be imagined. Why is it more than probable, that all men must die; that lead cannot, of itself, remain suspended in the air; that fire consumes wood, and is extinguished by water; unless it be, that these events are found agreeable to the laws of nature, and there is required a violation of these laws, or in other words, a miracle to prevent them? Nothing is esteemed a miracle, if it ever happen in the common course of nature. It is no miracle that a man, seemingly in good health, should die on a sudden: because such a kind of death, though more unusual than any other, has yet been frequently observed to happen. But it is a miracle, that a dead man should come to life; because that has never been observed in any age or country. There must, therefore, be a uniform experience against every miraculous event, otherwise the event would not merit that appellation....

The plain consequence is (and it is a general maxim worthy of our attention), 'That no testimony is sufficient to establish a miracle, unless the testimony be of such a kind, that its falsehood would be more miraculous, than the fact, which it endeavours to establish....' 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, which he relates, should really have happened. I weigh the one miracle against the other; and according to the superiority, which I discover, I pronounce my decision, and always reject the greater miracle. If the falsehood of his testimony would be more miraculous, than the event which he relates; then, and not till then, can he pretend to command my belief or opinion.

In the foregoing reasoning we have supposed, that the testimony, upon which a miracle is founded, may possibly amount to an entire proof, and that the falsehood of that testimony would be a real prodigy: But it is easy to shew, that we have been a great deal too liberal in our concession, and that there never was a miraculous event established on so full an evidence.

So, next time some apologist for religion or fan of the supernatural confronts you with that tired old canard of "you never know", just ask them to think about what's more likely, i.e. that,

a) all the natural laws of our universe were suspended momentarily just so that one evolved primate (of billions) on an insignificant speck of rock somewhere in a minor galaxy (of hundreds of billions) could learn something about themselves, or..

b) they are mistaken...