The so-called Exclusion argument (Kim 2000; Papineau 2004) about mental causation applies one premise that is typically accepted without much discussion: the thesis of causal completeness of the physical domain (CCP). In part one I evaluate Papineau’s (2001) argument for the CCP. I argue that this argument is not satisfying and that it is incomplete. The rest of the thesis is dedicated to an alternative to physicalism, namely ontological pluralism. Part two covers parts of Nancy Cartwright’s work (1983; 1999; 2007; forthcoming) and I account for her pluralism in causation. In part three I present and discuss metaphysical pluralism as argued for by John Dupré (1995). In the final section, I balance pluralism against physicalism. On the basis of that discussion I end with outlining an argument for ontological pluralism. My overall goal is mainly two things. I aim to show (i) that physicalism is not the only serious alternative to dualism, and (ii) that it is feasible to regard ontological pluralism, which I consider a type of philosophical materialism, as ‘the scientific metaphysics’.