The Science of Discworld IV

reject new evidence that global warming exists, whatever that may be, and stick to your existing beliefs. It may even lead you to reject all such evidence on the grounds that it has to be part of the hoax. If you don’t have strong beliefs either way, new evidence may cause you to modify your views. If you are already convinced about global warming, you may accept new evidence even if it is questionable.
    The same goes for religious beliefs. What we might call the epidemiology of religion shows that most people get their beliefs from their parents, close relatives, teachers (if of that persuasion), and priests. By the time they reach an age where they are capable of questioning what they have been taught, they may have built up such a strong system of beliefs that it is proof against any contrary evidence.
    So we use two ways of thinking, Systems 1 and 2. That’s suspiciously like Benford’s distinction. Are human-centred and universe-centred thinking related to the two components of Bayesian decisions – memory and data? It’s always tempting to line up dichotomies, assuming they carve things up in the same way, but in this case they don’t. Both memory and data are part of a quick-and-dirty intuitive decision process; they are different components that together drive System 1 thinking. System 2 is different, a much more conscious, deliberative analysis, assessing the evidence and
trying
– not always successfully – to ignore inbuilt prejudices. It’s not Bayesian.
    What does this tell us about belief? First, it explains why people have beliefs at all. They are a vital part of System 1 thinking, which has evolutionary survival value when snap judgements are essential. On the other hand, it also shows that this type of thinking may have deep flaws, whereby our beliefs override important data. If a snap judgement is not needed, it is better not to make one. Instead, we can employ System 2 thinking – often described as ‘rational’ or ‘analytical’ – and allow the data to change our beliefs if they fail to match reality.
    There is also the knotty question of belief versus disbelief. A UFO believer, for example, may argue that not believing in UFOs is merely another kind of belief. Namely, a belief that UFOs don’t exist. However, when virtually all of the alleged ‘evidence’ for UFOs turns out to be mistaken, or false, the contrary position isn’t a matter of belief at all. Zero belief in UFOs is not the same as 100% belief in the nonexistence of UFOs. Zero belief is an
absence
of belief, not an opposed form of belief. Similarly, science sets up a frameworkin which human beings consciously try to override their innate tendency to use System 1 thinking, because they know it can often be misleading. Scientists actively try to disprove the things they would like to be true.
    That’s not a belief system. It’s a disbelief system.
    fn1 Science fiction author A.E. Van Vogt coined the term in
Voyage of the Space Beagle
. He defined a nexialist to be someone who is good at joining together, in an orderly fashion, the knowledge of several fields of learning.
    fn2 It didn’t, anyway. The period concerned was just the first of an even vaster series of calendar cycles.
    fn3 Daisy Grewal, How critical thinkers lose their faith in God,
Scientific American
307 No. 1 (July 2012) 26.

TWENTY-ONE
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THE TURTLE MOVES!

    Marjorie drew breath.
    ‘My name, sir, is Marjorie Daw, and I am chief librarian for the borough of Four Farthings in London, England, er, on Earth. I am fluent in Latin and Greek, also in French, of course; and well versed in the patois of Essex …
whatever
. Today, I am also rather proud to have learned the library cataloguing language of Ook – a great revelation!’
    As she spoke, Marjorie was aware of the double doors at the end of the room swinging open, causing a susurrus among the audience. All eyes turned towards a tall white-haired man who looked rather like a farm worker; although, Marjorie thought, a farm worker would never walk with such presence, regardless of how many pigs he had. Moreover, the man strolling towards Lord Vetinari had a large hand-axe, which was attached to his body by a careful arrangement of leather strips.
    Lord Vetinari was watching the oncoming man with a smile on his face, while behind Marjorie the susurration had died away into silence, which was somehow a lot noisier by the time it hit the brain, where it thundered. The Patrician was on his feet as the