 According to Popper’s propensity interpretation, a probability \(p\) of an outcome of a certain type is a propensity of a repeatable experiment to produce outcomes of that type with limiting relative frequency \(p\). Again, infinitude is central to this interpretation, and its ugly head rears as it did for hypothetical frequentism. The best-system interpretation of probability, associated with Lewis (1994) and others, is also prey to problems if there are infinitely many events of a particular kind in the universe—for example, infinitely many coin tosses. As Elga (2004) shows, the interpretation’s central notion of fit is compromised. And even the subjective probabilities of idealized rational agents have tacit infinitary assumptions underlying them—for example, that the agents are logically omniscient, and their probability assignments are infinitely sharp (single real numbers). These assumptions have also been regarded as problematic, especially when modeling agents who are anything like us.