Sentence:  The textbook account of <WSD>epiphenomenalism</WSD> goes something like this. Although our thoughts, desires, and other mental states seem to affect what happens in the world, by bringing about changes in our behavior or subsequent mental states, this is "only an appearance", cast off by the real physical sequence of cause and effect that underlies our mental life. 
Meaning of the word marked with <WSD> tags:  The doctrine that mental states and processes are simply incidental effects of physiological events in the brain or nervous system and cannot themselves cause any effects in the material world.