 Our beliefs come in degrees; we believe some things more strongly than others. For instance, I believe that the sun will rise tomorrow very slightly more strongly than I believe that it will rise every morning for the coming week; and I believe both of these propositions much more strongly than I believe that there will be an earthquake tomorrow in Bristol. We call the strength or the degree of our belief in a proposition our credence in that proposition. Suppose I know that a die is to be rolled, and I believe that it will land on six more strongly than I believe that it will land on an even number. In this case, we would say that there is something wrong with my credences, for if it lands on six, it lands on an even number, and I ought not to believe a proposition more strongly than I believe a logical consequence of it. This follows from a popular doctrine in the epistemology of credences called Probabilism, which says that our credences at a given time ought to satisfy the axioms of the probability calculus (given in detail below). Since this says something about how our credences ought to be rather than how they in fact are, we call this an epistemic norm.