ABSTRACT
This chapter considers conditional probability from an ontological perspective, as opposed, for instance, to a logical or epistemic one. It looks at conditionals and their purported logical properties, including the material conditional, Lewisian counterfactuals and E. W. Adams’s Thesis. The conditionals have dispositions as their truthmakers and are better suited for a propensity based notion of conditional probability than the logical alternatives. Understood dispositionally, conditional probability is incompatible with the ontological commitments of Humeanism, and its logic is insufficiently represented by the ratio definition. The ratio analysis seems particularly well-suited for a Humean metaphysics, according to which there are no dispositions or other ontological connections between events. Causal uses will be defeasible under antecedent strengthening, showing that causation involves the dispositional modality, which permits exceptions under additive interference. Armed with ontology of real dispositions or powers, the path will be open for an alternative account of probability.
