  Recent philosophical work on mental properties has revealed that matters are not so simple, however. Mental properties are alleged to have, not just one, but up to four features that make their efficacy philosophically puzzling, no less problematic than mind–body interaction is for the Cartesian dualist. These features will be discussed in the following sections. Each feature makes it appear as though mental properties, or some important family of them, are irrelevant to the production of behavior. The threat is a form of epiphenomenalism: even if minds and mental events are causes, they are not causes as (or qua) mental.