Physicalism is standardly construed as a form of monism, on which all concrete phenomena fall under one fundamental type. It is natural to think that monism, and therefore physicalism, is committed to a supervenience claim. Monism is true only if all phenomena supervene on a certain fundamental type of phenomena. Physicalism, as a form of monism, specifies that these fundamental phenomena are physical. But some argue that physicalism might be true even if the world is disorderly, i.e., not ordered by (...) supervenience relations in the way commonly supposed (Montero in J Philos 110:92–110, 2013; Leuenberger in Inquiry 57:151–174, 2014; Montero and Brown in Topoi 37(3):523–532, 2018; Zhong in Philos Stud 178(5):1529–1544, 2021). Unless these authors intend to challenge the claim that physicalism is a type of monism—a claim so central to the dialectic in philosophy of mind that rejecting it risks changing the subject—they are committed to challenging a supervenience requirement for monism. We argue that monism entails that there are substantial supervenience relations among concrete phenomena: relations that would not obtain in a disorderly world. Our argument thus has implications for debates about physicalism and supervenience, and sheds light on an under-discussed issue: what is implied by classifying a theory in the philosophy of mind as a form of monism? We also argue that physicalism’s commitment to monism creates problems for _via negativa_ physicalism, on which the physical is characterized negatively. (shrink)