AAP 2026 CONFERENCE

Various philosophers have thought that the propensity interpretation of probability faces fatal objections. They include: “Propensities are mysterious.” “We don’t know how propensities behave.” “We do know that they don’t obey the probability calculus.” “Propensities are not Humean supervenient.” And “propensities do not vindicate the Principal Principle” (Lewis’s bridge principle between chances and rational credences).

I will revive the propensity interpretation. In a slogan: chances measure graded dispositions. More carefully, conditional chances measure graded dispositions to produce given outcomes, conditional on specifications of physical situations. Comparative dispositions are entirely familiar. My wine glass is more fragile than my beer mug; salt is more soluble than plastic. And I argue that we can get from comparative dispositions to numerical propensities that obey the probability calculus, answering all of the objections above (and more). Reports of the death of the propensity interpretation have been greatly exaggerated.