Against Bayesianism – David Deutsch
He doesn&#x27;t actually argue against the Bayesian view of statistics:<p>&gt; The word ‘Bayesianism’ is used for a variety of things, a whole spectrum of things at one end of which I have no quarrel with whatsoever and at the other end of which I think is just plain inductivism. So at the good end, Bayesianism is just a word for using conditional probabilities correctly. So if you find that your milkman was born in the same small village as you, and you are wondering what kind of a coincidence that is, and so on, you&#x27;ve got to look at the conditional probabilities, rather than the absolute probabilities. So there isn&#x27;t just one chance in so many million, but there&#x27;s a smaller chance.<p>His problem seems to be the extension of it to epistemology:<p>&gt; At the other end of the spectrum, a thing which is called Bayesianism is what I prefer to call ‘Bayesian epistemology’, because it&#x27;s the epistemology that&#x27;s wrong, not Bayes’ theorem. Bayes’ theorem is true enough. But Bayesian epistemology is just the name of a mistake. It&#x27;s a species of inductivism and currently the most popular species. But the idea of Bayesian epistemology is that, first of all, it completely swallows the justified true belief theory of knowledge.<p>His problem with inductivism is that when you follow it you don&#x27;t try to make theories more believable by getting rid of ones that don&#x27;t fit, but by confirming instances in which your theory does fit:<p>&gt; It&#x27;s inductivism with a particular measure of how strongly you believe a theory and with a particular kind of framework for how you justify theories: you justify theories by finding confirming instances. So that is a mistake because if theories had probabilities – which they don’t – then the probability of a theory (‘probability’ or ‘credence’, in this philosophy they’re identical, they’re synonymous)... if you find a confirming instance, the reason your credence goes up is because some of the theories that you that were previously consistent with the evidence are now ruled out.<p>&gt; And so there&#x27;s a deductive part of the theory whose credence goes up. But the instances never imply the theory. So you want to ask: “The part of the theory that&#x27;s not implied logically by the evidence – why does our credence for that go up?” Well, unfortunately it goes down. And that&#x27;s the thing that Popper and Miller proved in the 1980s. A colleague and I have been trying to write a paper about this for several years to explain why this is so in more understandable terms.<p>He cites this paper as an example of a proof, but claims it isn&#x27;t very approachable (which is why he is working on one with more understandable terms).<p><a href="https:&#x2F;&#x2F;sci-hub.3800808.com&#x2F;10.1038&#x2F;302687a0" rel="nofollow">https:&#x2F;&#x2F;sci-hub.3800808.com&#x2F;10.1038&#x2F;302687a0</a>