 Causal relations are normally thought to be objective features of the world. If they are to be captured in terms of probability theory, then probability assignments should represent some objective feature of the world. There are a number of attempts to interpret probabilities objectively, the most prominent being frequency interpretations and propensity interpretations. Most proponents of probabilistic theories of causation have understood probabilities in one of these two ways. Notable exceptions are Suppes (1970), who takes probability to be a feature of a model of a scientific theory; and Skyrms (1980), who understands the relevant probabilities to be the subjective probabilities of a certain kind of rational agent.