  The case of negative causation is especially challenging, not last because of the link between causation and such ethical and legal matters as passive killing (Bennett 1966; Green 1980; Foot 1984), good Samaritanism (Kleinig 1976) and, more generally, moral responsibility (Weinryb 1980; Walton 1980; Williams 1995; Fischer 1997; Clarke 2014). Here it is also customary to introduce finer-grained discriminations, distinguishing e.g. several ways in which an agent may fail to do something, e.g. (trying and) not succeeding, refraining, omitting, and allowing (Brand 1971; Milanich 1984; Hall 1984; Bach 2010). At least with regard to some such ways, it is very tempting to endorse a realist ontology. If so, the difficulty naturally arises of how and where to draw the line. For example, the realist about omissions will have to find a principled way of refraining from treating all omissions, including non-salient ones, as causes (Gorr 1979; Lewis 1986b, 2004; Thomson 2003; Menzies 2004; McGrath 2005; Sartorio 2009; Bernstein 2014). On the other hand, the antirealist will have to explain how one can account for such causal talk while holding on to the view that every causal situation develops from “positive factors alone” (Armstrong 1999). Some would insist that every alleged case of negative causation can be described in terms of positive causation (Laliberté 2013). Others—the majority—would resist ontological commitment by recasting the logical structure of the relevant causal claims in suitable ways, e.g. as causal statements about events that are counterfactually described (Hunt 2005), or as “quasi-causal” claims about what would have been a cause if the omitted event had happened (Dowe 2001), or as mere causal explanations in which the explanans does not stand to the explanandum as cause to effect (Beebee 2004; Varzi 2007; Lombard &amp; Hudson, in press).