Abstract
Think about a rubber ball. You say that it is disposed to be expanded when stretched. I say that it is disposed to contract when compressed. Then think about what dispositions the rubber ball has. Did we just attribute two different dispositions to the rubber ball, or is there only one and the same disposition under two different descriptions? The correct answer, it seems, is that there is only one. However, the disposition literature has been predominated by the verdict that you and I are ascribing two different dispositions to the rubber ball. This is not a coincidence, since this verdict is a consequence of the widely shared assumption that dispositions can be analyzed in terms of their stimulus conditions and manifestations. I challenge this assumption in the dissertation. The upshot is a version of non-Humean metaphysics that I call dispositional realism, according to which dispositions are real properties that explain the manifestation behaviors of their instances. At the heart of dispositional realism are multi-track dispositions, dispositions that can bring about their manifestations in multiple ways. I defend dispositional realism by arguing that the correct semantics of disposition terms is semantic externalism analogous to semantic externalism about natural kind terms; that explaining the status of quantitative law-like generalizations of fundamental physics requires an ontology of multi-track dispositions that are not analyzed by single-track dispositions; and that the truth-conditional content of our best science makes reference to multi-track dispositions.