To apply such a general probability to yield the chance of $e$, you need to specify the type $E$ of $e$ and also the reference class $C$. A probabilistic theory may offer alternative specifications when applied to determine the chance of $e$, in which case it becomes necessary to choose the appropriate specifications. Actuarial tables may be helpful when estimating the chance that you will live to be 100, but you differ in all kinds of ways from every individual whose death figures in those tables. What you want is the most complete available specification of *your* situation: this may include much irrelevant information, but it’s not necessary to exclude this since it won’t affect the chance anyway. In Minkowski space-time, the conceptual connection between chance ($Ch$) and the degree of belief ($Cr$) it prescribes is captured in this version of David Lewis’s Principal Principle that implicitly defines chance:[^5]

> The chance of $e$ at $p$, conditional on any information $I_{p}$ about the contents of $p$’s past light cone satisfies: $Cr_{p}(e/I_{p})=_{df}Ch_{p}(e)$.

Now consider an agent who accepts quantum theory and wishes to determine the chance of the event $e_{A}$ that the next photon detected by Alice registers as vertically polarized 