The Rationalist’s Road to Neutral Monism

Abstract The Principle of Sufficient Reason (PSR) is a cornerstone of rationalist metaphysics, yet many of its consequences remain underexplored. I argue that among these underexplored consequences is a striking variety of neutral monism, construed as the thesis that all entities share the same fundamental modal base. My argument proceeds in three stages. First, I motivate a commitment to attributes, metaphysically necessary properties that ultimately explain an entity’s modal profile. Second, I argue that the PSR supports the claim that every entity must instantiate every attribute. Third, I draw out the metaphysical implications of this conclusion: I show that it rules out substance dualism, versions of reductive and nonreductive physicalism, and idealism in favour of a neutral monist ontology.