Chapter 5      Part B. 

   The chief danger of Empiricism that Bayesians try to avoid is the insidious slip into dogmatism. Several times in the history of Science, empiricist-minded scientists have worked out and checked a theory so thoroughly that they have slipped into thinking that they have found an unshakeable truth. For example, physicists in the late 1800’s were in general agreement that there was little left to do in Physics. They believed that Newton and Maxwell, between them, had articulated all of the truths of all levels of the physical world, from the atomic to the cosmic. Einstein’s Theory of Relativity, of course, changed all of that. For many physicists of the old school, Relativity was a very rude shock.

    James Clerk Maxwell 

   Today, Physics is in a constant state of upheaval and uncertainty. There are still a few physicists who show a predilection for dogmatism, or we could say a longing for certainty. But most modern physicists are tentative and cautious. They’ve been let down so many times in the last fifty years by theories that once had seemed so promising, but that later were shown by experiment to be flawed, that most physicists have become permanently leery of any colleague who claims to have the “truth”.

It is regrettable that a similar caution has not caught hold of a few more of the physicists’ fellow scientists, especially the biologists. Darwinian evolution is indeed a powerful and impressive theory. It explains virtually all aspects of the living world that we currently know about. But it is still only a theory, which means that, like all theories, it should be viewed as tentative, not final or irrevocable. It just happens currently to have much more evidence to support it than do any of its competitors.

The larger point for our purposes here, however, is that Bayesians never endorse any one model as the last word on anything, and they never throw out any of the old models or theories entirely. Even those that are clearly wrong have things to teach us, and of the ones that are currently working well, we have to say that …they are currently working well. There are no final answers and no final versions of the truth in any model of reality for a Bayesian. The Theory of Evolution is only “currently working well”. 

By contrast, Rationalism has other problems, especially with Darwin’s Theory of Evolution.

For Plato, the whole idea of a canine genetic code that contained in it the instructions for the making of an ideal dog would have sounded appealing. It could have been written by the “Good”. But the idea that back a few geological ages ago there were no dogs, while there were some other animals that looked somewhat like dogs, but that also were not imperfect copies of an ideal dog, but more accurately should be called excellent examples of the species that they were supposed to be …no, Plato would have rejected such thinking. All dogs, for Plato, should be seen as poor copies of the ideal dog which exists in the pure, ideal dimension of the Good. The fossil records in the rocks don’t so much cast doubt on Plato’s idealism as belie it altogether. Gradual, incremental change in all species? No. Plato, with his commitment to the “forms”, would have confidently rejected the Theory of Evolution. 

In the meantime, Descartes’ form of Rationalism would have had serious difficulties with the mentally challenged. Do they have minds/souls or not? If they don’t get Math and Geometry, or in other words, if they don’t know and can’t discuss most of the ideas that Descartes called “clear and distinct”, then are they even human? And, of course, the abilities of the mentally challenged range from slightly below normal to severely mentally handicapped. At what point on this continuum do we cross the threshold between human and animal? Between the realm of the soul and that of mere matter, in other words? Descartes' answers are revolting to us at the start of the twenty-first century. 

  

To Descartes, animals didn’t have souls and therefore humans could do whatever they wished to them and not be violating any of his moral beliefs. In his own scientific work, he dissected dogs alive. Their screams weren’t, he claimed, evidence of real pain. They had no souls and, therefore, could not feel pain. The noise was more like the ringing of an alarm clock, a mechanical sound, nothing more. Generations of scientists after him did similar acts in the name of Science. (2.) 

  

But I am digressing. For now, we can simply put aside our regrets about the Rationalists and the Empiricists, and the inadequacies of their ways of looking at the world. We are ready to get back to Bayesianism.   

Notes 

2. http://boingboing.net/2011/06/30/richard-dawkins-on-v.html