“Given a particular observation, it may seem more obvious to frame a measurement by asking the question, “What can I conclude from this observation?” or, in probabilistic terms, “What is the probability X is true, given my observation?” But Bayes showed us that we could, instead, start with the question, “What is the probability of this observation if X were true?” The second form of the question is useful because the answer is often more straightforward and it leads to the answer to the first question. It also forces us to think about the probability of different observations given a particular hypothesis and what that means for interpreting an observation.”