   Busch (2003), Psillos (2006a) and Chakravartty (2003) all argue that individual objects are central to productive rather than Humean conceptions of causation and hence to any genuine explanation of change. Objects it is alleged provide the ‘active principle’ of change and causation. French (2006) replies to this charge invoking the idea of Ladyman (1998 and 2004) and French and Ladyman (2003) of modal structure, by which is meant the relationships among phenomena that pertain to necessity, possibility, potentiality, and probability. Ladyman and Ross (2007) defend a version of OSR according to which science describes the objective modal structure of the world, where the latter is ontologically fundamental, in the sense of not supervening on the intrinsic properties of a set of individuals.  They argue that causal structure is the pragmatically essential proxy for it in the special sciences (but not necessarily in fundamental physics). (Ladyman (2008) considers the causal exclusion argument in this context.) Nora Berenstain and Ladyman (2012) argue that a commitment to natural necessity is implicit in arguments for scientific realism and that realists including structural realists should be anti-Humean and believe in objective modal structure. See also Esfeld (2009) and for a Humean take on structural realism, Lyre (2010). The structure of dispositions described by Mumford (2004) and Psillos's (2003) idea of nomological structure are cognate to the idea of modal structure. Giere (1985) first suggested that a form of structural realism was the result of conjoining modal realism with constructive empiricism. There is a forthcoming special issue of Synthese dedicated to examining the relationship between structuralism and causation. See also the 'final section' of articles on single modality and causality in structural realism in Landry and Rickles (2012).