The view that some feature of a situation arises in virtue of others, but itself has no causal powers. In the philosophy of mind this means that while there exist mental events, states of consciousness, and experiences, they have themselves no causal powers, and produce no effect on the physical world. The analogy sometimes used is that of the whistle on the engine, that makes the sound (corresponding to experience), but plays no part in making the machinery move. Epiphenomenalism is a drastic solution to the major difficulty of reconciling the existence of mind with the fact that according to physics itself only a physical event can cause another physical event. An epiphenomenalist may accept one-way causation, whereby physical events produce mental events, or may prefer some kind of parallelism, avoiding causation either between mind and body or between body and mind (see occasionalism). A major problem for epiphenomenalism is that if mental events have no causal relationships it is not clear that they can be objects of memory, or even awareness. See also base and superstructure, private language argument.