"The most powerful argument against epiphenomenalism is that it is self contradictory: If we have knowledge about epiphenomenalism, then we know about the existence of the mind, but if epiphenomenalism were correct, then we should not have any knowledge about the mind, as it does not affect anything physical. [9]" -- WP

"Epiphenomenalism is absurd; it is just plain obvious that our pains, our thoughts, and our feelings make a difference to our (evidently physical) behavior; it is impossible to believe that all our behavior could be just as it is even if there were no pains, thoughts, or feelings. (Taylor, 1963 and subsequent editions, offers a representative statement.)"--SEP