Abstract

I present an argument against the view that the additivity of mass (i.e., the property according to which a composite object’s mass is the “sum” of its parts’) is metaphysically independent of dynamical laws governing massive bodies. In particular, taking additivity to be independent of dynamics commits you to widespread unexplained correlations between the mass properties of composites and the dynamic behavior of massive bodies. The second half of the paper extends this explanatory worry, showing that the very same considerations apply to aspects of mass’s quantitative structure. This gives rise to a new and powerful objection to certain influential theories about the fundamental structure of physical quantities —most notably the magnitude realism of Peacocke (2019) and the second-order absolutist accounts defended by Mundy (1987) and Eddon (2013b).