We discussed quantum theory yesterday. Now it is time to remind ourselves of the other half of our proposed mash-up. 'Bayesianism' is an approach to probability theory that begins with subjectivity, with somebody's guess about what is the likelihood of an event. It then discusses how an individual having certain circumstances may change his beliefs rationally, and (assuming he has beliefs on more than one question) may keep them consistent with one another -- or, in other words, how he may keep his view of the world coherent. The chief rival of Bayesianism is "frequentism." This treats probability as an objective fact in the world, another name for the frequency of some outcomes vis-a-vis others. I've discussed this difference before. But ... what does it have to do with quantum theory? Collapse the Function for your own Damned Self With a Bayesian approach we get a take on quantum theory that doesn't shrug its shoulders at the "what is rea...