An epiphenomenon is a secondary phenomenon that occurs alongside a primary phenomenon. A phenomenon (plural: phenomena) is an observable event, especially something special (literally something that can be seen from the Greek word phainomenon = observable). ...

Often, a causal relationship between the phenomena is implied: the epiphenomenon is a consequence of the primary phenomenon. In medicine, this relationship is typically not implied: an epiphenomenon may occur independently, and is merely called an epiphenomenon because it is not the primary phenomenon under study. (A side-effect is a specific kind of epiphenomenon that does occur as a consequence.) The philosophical concept of causality or causation refers to the set of all particular causal or cause-and-effect relations. ... Medicine is a branch of health science concerned with restoring and maintaining health. ... A side-effect is any effect other than an intended primary effect. ...

In philosophy of mind, epiphenomenalism is the view that mental phenomena are caused by physical phenomena, and cannot cause anything themselves. It was probably first mentioned by T. H. Huxley in 1874. This article needs cleanup. ... Epiphenomenalism is the view in philosophy of mind according to which physical events have mental effects, but mental events have no physical effects. ... The mind is the term most commonly used to describe the higher functions of the human brain, particularly those of which humans are subjectively conscious, such as personality, thought, reason, memory, intelligence and emotion. ... Thomas Huxley Thomas Henry Huxley F.R.S. (May 4, 1825 – June 29, 1895) was a British biologist, known as Darwins Bulldog for his defence of Charles Darwins theory of evolution. ...

References

Huxley, T. H. (1874). On the Hypothesis that Animals are Automata, and its History, The Fortnightly Review, n.s.16:555-580. Reprinted in Method and Results: Essays by Thomas H. Huxley (New York: D. Appleton and Company, 1898).