Chapter 6.                           (continued) 

 

                                                             execution by hanging (Canada 1902) 

This Bayesian model of how we think is so radical that at first it eludes us. To each individual, the idea that she is continually adjusting her entire mindset, and that no parts of it, not even her deepest ideas of who she is or what reality is, can ever be fully trusted is disturbing to say the least. Doubting our most basic ideas is flirting on the edge of mental illness. Even considering the possibility is upsetting. But this radical Bayesian view is certainly the one I arrive at when I look back honestly over the changes I have undergone in my own life. The Bayesian model of how a “self” is formed, and how it evolves as the organism ages, fits the set of memories that I call “myself” exactly.

Thomas Kuhn was the most famous of the philosophers who have examined the processes by which people adopt a new theory, model, or way of knowing. His works focused only on how scientists adopt a new scientific model, but his conclusions can be applied to all human thinking. His most famous book proposes that all our ways of knowing, even our most cherished ones, are tentative and arbitrary.² Under his model of how human knowledge grows, humans advance from an obsolete idea or model to a newer, more comprehensive one by paradigm shifts— that is by leaps and starts rather than in a steady march of gradually growing enlightenment. We “get”, and then start to think under, a new model for organizing our thoughts by a kind of conversion experience, not by a gradual process of persuasion and growing understanding.

                            

Caution and vigilance seem to be the only rational attitudes to take under such a view of the universe and the human place in it. To many people, the idea that all of the mind’s systems—and its systems for organizing systems and perhaps even its overriding operating system, its sanity—are tentative and are subject to constant revision seems even more than disturbing; it seems absurd. But then again, cognitive dissonance theory would lead us to predict that humans would quickly dismiss such a scary picture of themselves. We don’t like to see ourselves as lacking in any unshakeable principles or beliefs. However, evidence and experience suggest we are indeed almost completely lacking in fixed concepts or beliefs, and we do nearly always evolve personally in those scary ways. (Why I say nearly always and almost completely will become clear shortly.)

Now, at this point in the discussion, opponents of Bayesianism begin to marshal their forces. Critics of Bayesianism give several varied reasons for continuing to disagree with the Bayesian model, but I want to deal with just two of the most telling—one is practical and evidence-based, and the other, which I’ll discuss in the next chapter, is purely theoretical.

In the first place, say the critics, Bayesianism simply can’t be an accurate model of how humans think because humans violate Bayesian principles of rationality every day. Every day, we commit acts that are at odds with what both reasoning and experience have shown us is rational. Some societies still execute criminals. Men continue to bully and exploit, even beat, women. Some adults still spank children. We fear people who look different from us on no other grounds than that they look different from us. We shun them even when we have evidence showing there are many trustworthy individuals in that other group and many untrustworthy ones in the group of people who look like us. We do these things even when research indicates that such behaviour and beliefs are counterproductive.

Over and over, we act in ways that are illogical by Bayesianism’s own standards. We stake the best of our human and material resources on ways of behaving that both reasoning and evidence say are not likely to work. Can Bayesianism account for these glaring bits of evidence that are inconsistent with its model of human thinking?