Chapter 7.                                              (continued) 

And what of the spirit of Bayesianism? Bayesian thinking requires us to be willing to float all of our concepts, even our most deeply held ones. Some are more central, and we can stand on them more often and with more confidence. A few we may believe almost, but not quite, absolutely. But in the end, none of our concepts is irreplaceable.

For humans, the mind is our means of surviving. If it has to, it will adapt to almost anything. We gamble heavily on the concepts we routinely use to organize our sense data and memories of sense data.

I use my concepts to organize both the memories already stored in my brain and the new sense data that are flooding into my brain all the time. I keep trying to acquire more concepts, including concepts for organizing other concepts that will enable me to utilize my memories more efficiently to make faster and better decisions and to act increasingly effectively. In this constant, restless, searching mental life of mine, I never trust anything absolutely. If I did, a simple magic show would mesmerize and paralyze me. Or reduce me to catatonia.

When I see elephants disappear, women get sawn in half, and men defy gravity, and all come through their ordeals in fine shape, some of my most basic and trusted concepts are obviously being violated. But I choose to stand by my concepts in almost every such case, not because I am certain they are perfect but because they have been tested and found effective over so many trials and for so long that I’m willing to keep gambling on them. I don’t know whether they are “sure things,” but they do seem like the most promising of the options available to me.

     

                                        Harry Houdini with his “disappearing” elephant, Jennie.

Life is constantly making demands on me to move and keep moving. I have to gamble on some things; I go with my best horses. And sometimes, I change my mind.

This mental flexibility on my part means that the critics of Bayesianism simply haven’t grasped its spirit. Bayesianism is telling us pretty much what Thomas Kuhn said in The Structure of Scientific Revolutions. We are constantly adjusting our concepts to try to make our ways of dealing with reality more effective.

And when a researcher begins to grasp a new hypothesis and the model or theory it is based on, the resulting experience is like a philosophical or religious “awakening”—profound, all-encompassing, and even life-altering. Everything "changes" when we accept a new model or theory—because we change. In order to “get it,” we have to change. We have to eliminate some of the old beliefs from our familiar background set.

And what of the shifting nature of our view of reality and the gambling spirit that is implicit in the Bayesian model? The general tone of all our experiences tells us that this overall view of our world and ourselves, though it may seem scary or perhaps, for more confident individuals, challenging—is just life.

 

We have now arrived at a point where we can feel confident that Bayesianism gives us a solid base on which to build further reasoning. Solid enough to use and so get on with all of the other thinking that has to be done. It can answer its critics decisively—both those who attack it with real-world counterexamples and those who attack it with pure logic.

For now, then, let us be content to summarize our points so far in a new chapter devoted solely to that summing up.

Notes

1. Thomas Kuhn, The Structure of Scientific Revolutions (Chicago: The University of Chicago Press, 3rd ed., 1996).