Thomas Bayes’ first great contribution was to use probability as an expression of our lack of knowledge about the world or, equivalently, our ignorance about what is currently going on. He showed that probability can be used not only for future events subject to random chance – aleatory uncertainty, to use the term introduced in Chapter 8 – but also for events which are true, and might well be known to some people, but that we are not privy to – so-called epistemic uncertainty.
