  Now, however, we are again confronted with the threat of epiphenomenalism. If mental properties are not physical, how could they make a causal difference? Whenever any mental (functional) property M is instantiated, it will be realized by some particular physical property P. This physical property is unproblematically relevant to producing various behavioral effects. But then what causal work is left for M to do? It seems to be causally idle, “excluded” by the work of P.