Structural Parsimony

Many metaphysicians often appeal to Hume’s dictum (HD), according to which there are no necessary connections between distinct entities (or states of entities), in order to resist theories that commit us to such connections. Some have argued that HD is an unsupported dogma of metaphysics. But theories that commit us to necessary connections between distinct goings-on can also be resisted by invoking a normative twist on HD, which I call the Humean Solvent (HS): “Do not connect distinct entities (or states of entities) beyond necessity”. HS is a principle of structural parsimony – assuming that a theory is structurally more parsimonious than another when the latter is committed to a more connected ontology than the former is. Just as Ockham’s ‘razor’ encourages us to cut down superfluous ontological commitments, the Humean ‘solvent’ encourages us to dissolve dispensable metaphysical glue: we ought not to glue elements of our ontology beyond necessity. HS has both a qualitative and a quantitative dimension: qualitatively, it encourages us to avoid using metaphysical glues that are unnecessarily strong, the strongest of which being metaphysically necessary connections; quantitatively, it encourages us not to metaphysically glue things that need no gluing. Thus, given HS, other things being equal, what is worst is a theory that entails that everything is metaphysically necessarily connected to anything else and what is best is a theory that leaves all things loose and separable. In this paper, I will first compare HD and HS as grounds for paradigmatic Humean doctrines in contemporary metaphysics, then I will argue that structural parsimony is neither a variety of ontological nor of ideological parsimony; finally, I will offer an argument for HS.