  This appears to strip functional properties of their causal efficacy. Why? One line of thought appeals to Hume’s celebrated doctrine that there can be no necessary connections between distinct existences. A mental property and its would-be effect are distinct, yet functionalism entails that they enjoy a necessary connection. On the Humean doctrine, such a connection could not be causal. Another, closely related, version of the problem requires that causal relations be subsumed by empirical laws. But there are no such laws available for functional properties if all of the relevant generalizations are analytic and vacuous. (The foregoing argument in either version threatens to generalize to all dispositional properties: see  dispositions, §6. For the problem aimed at functionalism in particular, see Block 1990; Rupert 2006; functionalism, §5.2.)