# Epiphenomenalism_First published Mon Jan 18, 1999; substantive revision Thu Jun 15, 2023_Epiphenomenalism is the view that mental events are caused by physical events in the brain, but have no effects upon any physical events. Behavior is caused by muscles that contract upon receiving neural impulses, and neural impulses are generated by input from other neurons or from sense organs. On the epiphenomenalist view, mental events play no causal role in this process. Huxley (1874), who held the view, compared mental events to a steam whistle that contributes nothing to the work of a locomotive. James (1879), who rejected the view, characterized epiphenomenalists’ mental events as not affecting the brain activity that produces them “any more than a shadow reacts upon the steps of the traveller whom it accompanies”.Ancient theories of the soul gave rise to debates among Aristotle’s successors that have a strong resemblance to some contemporary discussions of the efficacy of mental events (Caston, 1997). The modern discussion of epiphenomenalism, however, traces back to a 19th century context, in which a dualistic view of mental events was assumed to be correct. The first part of our discussion — Traditional Arguments — will be phrased in a style that reflects this dualistic presupposition. By contrast, many contemporary discussions work within a background assumption of the preferability of materialist monism. One might have supposed that this position would have put an end to the need to investigate epiphenomenalism; but, as we shall see under Arguments in the Age of Materialism, such a supposition is far from being the case. A brief outline of both discussions follows.* * *## 1. Traditional Arguments (A) ProMany philosophers recognize a distinction between two kinds of mental events. (A) The first goes by many names, e.g., phenomenal experiences, occurrences of qualitative consciousness, the what-it-is-like of experience, [qualia](https://plato.stanford.edu/entries/qualia/). Pains, afterimages, and tastes can serve as examples. (B) Mental events of the second kind are occurrent propositional attitudes, e.g., (occurrent) beliefs and desires. Arguments about epiphenomenalism may concern either type of mental event, and (as made clear in Campbell 1970) it should not be assumed that an argument given for one type can be rephrased without loss for the other. The two types can often be connected, however, through beliefs that one has one’s experiences. Thus, if it is held that pains have no physical effects, then one must say either (i) pains do not cause beliefs that one is in pain, or (ii) beliefs that one is in pain are epiphenomenal. For, if pains caused beliefs that one is in pain, and the latter had physical effects, then pains would, after all, have effects in the physical world (albeit indirectly). But epiphenomenalism says mental events have _no_ effects in the physical world.[[1](https://plato.stanford.edu/entries/epiphenomenalism/notes.html#note-1)]The central motivation for epiphenomenalism lies in the premise that whenever there is a sufficient cause of a physical event, there is a sufficient _physical_ cause of that 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.One may try to rescue mental efficacy by supposing that whenever there is a mental effect in the physical world there is _also_ a physical force that is a sufficient cause of the effect. This view, however, both offends Occamist principles and fails to satisfy the leading anti-epiphenomenalist intuition, namely, that the mental _makes a difference_ to the physical, i.e., that it leads to behavior that would not have happened in absence of the mental. The view also leads to an epistemological problem: If there is always a sufficient physical cause for whatever a mental event is supposed to produce, then one could never be in a position where one _needs_ to suppose there is anything non-physical at work, and thus there could never be any reason to introduce mental causes into one’s account of neural events or behavior.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.Further support for epiphenomenalism can be derived from the fact, noted by Wilhelm Wundt (1912), that “each simple sensation is joined to a very complicated combination of peripheral and central nerve processes”, together with the fact that the causes of behavior are likewise complex neural events. This latter fact makes it natural to look for complex events throughout the causal chain leading to behavior; and these can be found in the neural events that are required for the occurrence of simple sensations. The sensations themselves could not contribute to behavior without first having neural effects that are more complex than themselves. Thus an anti-epiphenomenalist stance would require us to prefer the hypothesis that simple sensations cause (relatively) complex neural events over the hypothesis that complex neural events (that are required in any case for the causation of sensations) are adequate to cause the neural events required for the causation of behavior.