Abstract
The aim of Modality and Explanatory Reasoning (MER) is to shed light on metaphysical
necessity and the broader class of modal properties to which it belongs. This topic is
approached with two goals: to develop a new and reductive analysis of modality, and to
understand the purpose and origin of modal thought. I argue that a proper understanding
of modality requires us to reconceptualize its relationship to causation and other forms of
explanation such as grounding, a relation that connects metaphysically fundamental facts
to non-fundamental ones. While many philosophers have tried to give modal analyses of
causation and explanation, often in counterfactual terms, I argue that we obtain a more
plausible, explanatorily powerful and unified theory if we regard explanation as more
fundamental than modality. The function of modal thought is to facilitate a common type
of thought experiment—counterfactual reasoning—that allows us to investigate
explanatory connections and which is closely related to the controlled experiments of
empirical science. Necessity is defined in terms of explanation, and modal facts often
reflect underlying facts about explanatory relationships. The study of modal facts is
important for philosophy not because these facts are of much metaphysical interest in
their own right, but largely because they provide evidence about explanatory connections