About a month ago The Age published an opinion piece I wrote under the title “Do you hold a Bayesian or Boolean worldview?“. I had submitted it under the title “Madmen in Authority,” and it opened by discussing two men in authority who are/were each mad in their own way – Maurice Newman, influential Australian businessman and climate denier, and Cuban dictator Fidel Castro. Both men had professed to be totally certain about issues on which any reasonable person ought to have had serious doubts given the very substantial counter-evidence.
Their dogmatic attitudes seemed to exemplify a kind of crude epistemological viewpoint I call “Booleanism,” in contrast with a more sophisticated “Bayesianism”. Here is the philosophical core of the short opinion piece:
On economic matters, Keynes said: “Practical men who believe themselves to be quite exempt from any intellectual influence, are usually the slaves of some defunct economist. Madmen in authority, who hear voices in the air, are distilling their frenzy from some academic scribbler of a few years back.”
Similarly, on matters of truth and evidence, we are usually unwittingly beholden to our background epistemology (theory of knowledge), partially shaped by unknown theorists from centuries past.
One such theory of knowledge we can call Boolean, after the 19th century English logician George Boole. He was responsible for what is now known as Boolean algebra, the binary logic which underpins the computing revolution.
In the Boolean worldview, the world is organised into basic situations such as Sydney being north of Melbourne. Such situations are facts. Truth is correspondence to facts. That is, if a belief matches a fact, it is objectively true; if not, it is objectively false. If you and I disagree, one of us must be right, the other wrong; and if I know I’m right, then I know you’re wrong. Totally wrong.
This worldview underpins Castro’s extreme confidence. Either JFK was killed by an anti-Castro/CIA conspiracy or he wasn’t; and if he was, then Castro is 100 per cent right. Who needs doubt?
An alternative theory of knowledge has roots in the work of another important English figure, the Reverend Thomas Bayes. He is famous for Bayes’ Theorem, a basic law of probability governing how to modify one’s beliefs when new evidence arrives.
In the Bayesian worldview, beliefs are not simply true or false, but more or less probable. That is, we can be more or less confident that they are true, given how they relate to our other beliefs and how confident we are in them. If you and I disagree about the cause of climate change, it is not a matter of me being wholly right and you being wholly wrong, but about the differing levels of confidence we have in a range of hypotheses.
Scientists are generally Bayesians, if not self-consciously, at least in their pronouncements. For example, the IPCC refrains from claiming certainty that climate change is human-caused; it says instead that it has 95 per cent confidence that human activities are a major cause.