 How can mental goings-on bring about physical effects, as they seem to do, given that the physical realizers of mental goings-on are already sufficient to cause these effects? This question gives rise to the problem of mental (more generally, higher-level) causation, encoding two threats: first, that mental properties, if efficacious, give rise to problematic causal overdetermination; second, that avoiding overdetermination requires that mental properties be causally excluded by their realizers. Overdetermination and exclusion are avoided if mental and physical goings-on are identical, but in that case it seems that mental goings-on are not efficacious qua mental (see Horgan 1989); as Yablo puts it: “Mental events are effective, maybe, but not by way of their mental properties” (1992: 249). Moreover, type identity seems at odds with the multiple realizability of mental properties.