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The central motivation for epiphenomenalism lies in the premise that anything that can causally contribute to a physical event must itself be a physical event. If a mental event is something other than a physical event, then for it to make any causal contribution of its own in the physical world would require a violation of physical law. Descartes' (1649) interactionist model proposed that nonphysical events could cause small changes in the shape of the pineal gland. But such nonphysical effects, however slight, would mean that the physical account of motion is false — for that account says that there will be no such change of shape unless there is a physical force that causes it.

Many contemporary thinkers would respond to the central motivation for epiphenomenalism by denying its dualistic presupposition, i.e., by holding that mental events are identical with physical events, and may therefore have physical effects. Questions that remain for such physicalistic views will be explained in section 3. For now, it should be noted that the argument stated in the previous two paragraphs is not supposed to be an argument for dualism, but only for adopting epiphenomenalism, once dualism is accepted.

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.)