Feb 272014

How’s this for conclusive evidence?

Mr Shimkus, a Republican from rural Illinois, is not just staunchly pro-industry, anti-regulation and sceptical of claims that man’s activities menace the planet. He also brings his Bible to work. At a hearing on greenhouse gases, he opened it and quoted God’s words to Noah after the Flood. “Never again will I destroy all living creatures,” God promised. This, said Mr Shimkus, was “infallible” proof that neither man’s actions nor rising flood waters will destroy the Earth. So let’s not worry too much about global warming (The Economist, 22 February).

A little delving is enough to put some nuance around the statement and thankfully appreciate that US Representative John Shimkus is not a complete lunatic. Same for George W. Bush, whose religious faith admittedly contributed to make him Dead Certain about many hypotheses that turned out to be false.

The crux of the matter is that, in the absence of truly conclusive evidence, our beliefs remain influenced, to a more or less large extent, by our priors. And the closer our priors are to one of the two boundaries of the probability spectrum, the larger is the amount of evidence that we require to move away from them. In the extreme, Faith (BR=1 or 0) is impermeable to any amount of evidence. That’s why, at least on earthly matters, we should make a point of staying away from Faith, and remain open to answer Popper’s question: What reasonable evidence do you require that would be enough for you to change your mind? If you think a hypothesis is very likely to be true, you should define evidence that could disconfirm it and potentially prove it false. If you think the hypothesis is very likely to be false – as with Mr Shimkus and global warming – you should define evidence that could confirm it and potentially prove it true. The exact opposite of trying to use your faith to prove it false.

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