A Chance for Possibility defends the view that the objective modal realm is tripartite: truths about possible worlds supervene on modal truths, which in turn supervene on truths about objective chances. An understanding of supervenience in terms of grounding is developed which — unlike the standard modal characterization — allows the question of what modal truths supervene on to have a non-trivial answer. Relying on this understanding, a negative result is established: modal truths do not supervene on truths about possible worlds, whether possible worlds are conceived of as Lewisian concreta or as abstract objects of some kind. Instead, a conception of pleonastic possible worlds is developed that reverses the direction of supervenience. On the basis of linguistic considerations concerning our use of natural language ‘might’ and ‘might have’ sentences, Steinberg finally argues that truths about objective chances are able to provide a supervenience base for modal truths. A Chance for Possibility is an investigation in analytic metaphysics, drawing on related work in the philosophy of logic and language as well as linguistics. It provides a detailed case study for the fruitful use of a notion of grounding in the clarification and evaluation of longstanding philosophical issues.