Fallacy of the single cause

The fallacy of the single cause, also known as complex cause, causal oversimplification, causal reductionism, and reduction fallacy, is a fallacy of questionable cause that occurs when it is assumed that there is a single, simple cause of an outcome when in reality it may have been caused by a number of only jointly sufficient causes.

It can be logically reduced to: X caused Y. Therefore, X was the only cause of Y (although A,B,C...etc. also contributed to Y.)

Causal oversimplification is a specific kind of false dilemma where conjoint possibilities are ignored. In other words, the possible causes are assumed to be "A or B or C" when "A and B and C" or "A and B and not C" (etc.) are not taken into consideration.

Often after a tragedy it is asked, "What was the cause of this?" Such language implies that there is one cause, when instead there was probably a large number of contributing factors. However, having produced a list of several contributing factors, it may be worthwhile to look for the strongest of the factors, or a single cause underlying several of them. A need for simplification may be perceived in order to make the explanation of the tragedy operational, so that responsible authorities can be seen to have taken action.

For instance, after a school shooting, editorialists debate whether it was caused by the shooter's parents, violence in media, stress on students, or the accessibility of guns. In fact, many different causes—including some of those—may all have necessarily contributed. Similarly, the music industry might claim that peer-to-peer file sharing is the cause of a loss in profit whereas factors such as a growing video game market and economic depression are also likely to be major factors.

A notable scientific example of what can happen when this kind of fallacy is identified and resolved is the development in economics of the Coase theorem. In neuroscience, this fallacy is in evidence when a scientist electrically stimulates one area of the brain, observes an effect (say, the patient blinks his eyes), and assumes that the brain area is sufficient for the movement (the essence of blinking) rather than merely necessary.

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