|Parallelists, in philosophy, are dualists, holding that mental and physical phenomena are distinct. One traditional problem for those who hold that mental and physical phenomena are distinct is the difficulty of explaining how non-physical mental phenomena and non-mental physical phenomena could causally interact. Parallelists respond to this problem by bluntly denying that the mental and physical causally interact. Physical phenomena such as damage to the body do not cause mental phenomena such as pains, and mental phenomena such as pains do not cause physical phenomena such as winces. Rather, mental phenomena are only causally related to other mental phenomena and physical phenomena are only causally related to other physical phenomena. But the mental to mental and physical to physical causal chains run in parallel, giving rise to the illusion that mental and physical phenomena do causally interact.
An analogy makes clear that two causal chains which run in parallel may seem to be causally related even though they are not. Suppose that the causal chains which run through two time-keeping devices are perfectly correlated. So whenever the traditional clock with two hands shows one o\'clock, the electric beeper with no clock face beeps once, whenever the traditional clock shows two o\'clock, the electric beeper beeps twice, and so on. This could give rise to the impression that traditional clock\'s showing the hour causes the beeping. But of course, the two time-keeping devices do not causally influence the other. It is just that some (although not all) of the events in the causal chains which run through each device are so correlated as to give rise to the illusion that they causally interact. AJ
See also dualism; epiphenomenalism; interactionism; mind-body problem.Further reading C.D. Broad, The Mind and Its Place in Nature.