Jon Williamson (Kent) gives a talk at the MCMP Colloquium (8 October, 2014) titled "The Principal Principle implies the Principle of Indifference". Abstract: I'll argue that David Lewis' Principal Principle implies a version of the Principle of Indifference. The same is true for similar principles which need to appeal to the concept of admissibility. Such principles are thus in accord with objective Bayesianism, but in tension with subjective Bayesianism. One might try to avoid this conclusion by disavowing the link between conditional beliefs and conditional probabilities that is almost universally endorsed by Bayesians. I'll explain why this move offers no succour to the subjectivist.