  The functionalist has a number of options available, some of them mirroring solutions to the Exclusion Problem (Rupert 2006 provides a critical survey). For example, a functionalist could settle for a weaker, explanatory role for functional properties, leaving causal efficacy to the realizers of functional states (§6.4; see, e.g., Segal 2009; compare Roth and Cummins 2014). Or a functionalist might identify states of mind with their realizers (§6.5); indeed, some of the early functionalists were identity theorists (Lewis 1966, 1994; Armstrong 1968/1993). This would permit the sort of re-description that the more mainstream version of functionalism apparently blocks. A third option is to look for non-vacuous, empirical generalizations subsuming functional properties (Antony and Levine 1997). Yet a fourth option rejects the Humean doctrine, permitting necessary connections between a causally efficacious property and its effect. Such a proposal would find a home in the more general “causal theory of properties” defended by Shoemaker (1980, 1998) and others.