 Because non-reductive physicalist theories attempt to both retain the ontological distinction between mind and body and try to solve the "surfeit of explanations puzzle" in some way; critics often see this as a paradox and point out the similarities to epiphenomenalism, in that it is the brain that is seen as the root "cause" not the mind, and the mind seems to be rendered inert.Epiphenomenalism regards one or more mental states as the byproduct of physical brain states, having no influence on physical states.The interaction is one-way (solving the "surfeit of explanations puzzle") but leaving us with non-reducible mental states (as a byproduct of brain states) – causally reducible, but ontologically irreducible to physical states.