Does Probability Require a Single History?

Abstract: Everettian quantum mechanics is often said to lack coherent probability because every possible measurement result occurs. If all of them exist globally, what is probability supposed to be a probability of? This paper defends an axiomatic answer: normalized Born measure is postulated as objective probability over the records borne by an observer's future continuations. A collapse law assigns the same probabilities to possible global outcomes. Neither theory derives the probabilities from its ontology. I relate this minimal proposal to earlier axiomatic accounts, separate it from their accompanying theories of personal persistence, and defend it against recent arguments that the axiomatic route cannot succeed. At the level of recorded results, the Everettian law supports the same predictions and empirical inferences as the collapse law, despite the theories' different ontologies.