Metaphysics and Necessity

Shamik Dasgupta (Princeton University )

There is an attractive Leibnizian line of thought on which one dispenses with "excess" structure. This  line of thought leads to various sparse metaphysical views: e.g. the view that all motion is grounded in relative motion, that all facts about mass grounded in mass relations, and so on. By the popular principle of Necessitation -- that grounds necessitate what they ground -- these sparse metaphysical views entail a restricted possibility space: that there is no distinction between worlds that differ in a uniform velocity boost, or between worlds in which masses are uniformly doubled, and so on. But this restriction on possibility space can sometimes be a vice. For example, David Baker has argued that, in the case of mass, it implies that one's fundamental physics is pathologically indeterministic. In response, I think the sparse metaphysician should distinguish between different senses of "possibility". There is a sense of "possible" on which Necessitation is correct, and on which these sparse metaphysical views imply a restricted possibility space. But that is not the same sense of "possible" in which determinism is properly defined. If that's right, then sparse metaphysical views do not (in the relevant sense) yield a pathologically indeterministic physics after all. The challenge is to clearly articulate these difference senses of "possibility" and argue that the move is not ad hoc.