A single cause is identified when the effect is actually caused by a number of interacting objects or events. The result is oversimplification or reductionism. A variation of this fallacy is the feedback loop, where the effect is itself a part of the cause. Many of the intractable disagreements we have debated for generations are so difficult because it is so difficult to isolate the relevant or primary causes of an effect.
- "A widespread version of this fallacy is seen in arguments that blame individual figures for broad historical events, for example, 'Eisenhower caused America to be involved in the Vietnam War.' Such a claim ignores the cold war ethos, the long history of colonialism in Southeast Asia, and a multitude of other factors. When you reduce a complex sequence of events to a simple and single cause — or assign a simple effect to a complex cause — you will virtually always be wrong." (Rosenwasser and Stephen, Writing Analytically, p. 142)
- The Challenger explosion was caused by the cold weather. (True, however, it would not have occurred had the O-rings been properly constructed.)
- "When considering a whole country and a five year period ... In Tanzania, several hundred specific interventions have been recorded in areas as different as basic education, electoral processes, or port infrastructure. Funds have been disbursed through five distinct channels, from integrated support to the national budget to subsidizing local non-governmental organizations. No doubt the subject of the evaluation was complicated. ¶ Some cause-and-effect chains were simple in the sense that they were short and linear. For instance, ... the building of a consistent road network with the assumption that the rural population would get a faster and cheaper access to basic services, which in turn would reduce rural poverty. ¶ However, a majority of cause-and-effect chains were complex. For instance, it was assumed that the [European Commission] could coordinate with other donors in developing a harmonized dialogue with the government on road policy, with the expected consequences that this policy be reformed, sustainable financial resources be devoted to road maintenance, local authorities benefit from a substantial part of these resources, they are responsive to the needs of the poorest rural areas, they manage to properly maintain the rural road network, the access to basic services is facilitated in remote rural areas, and rural poverty is eventually reduced. In this case, the chain of causes and effects is to only long, but is also complex in the sense that it involves causality loops, for example, interactions between the Government and development partners, interactions between the Government and local authorities, responsiveness of local authorities to the population needs, etc. (Toulemonde, Carpenter, and Raffier, "Coping with the Evaluability Barrier" in Evaluating the Complex, p. 123.)
- "[A] great classicist, J.B. Bury ... eliminated depopulation, the Christian religion, and the fiscal system as causes of the dismemberment of the Roman empire. 'If these or any of them were responsible for [the Empire's] dismemberment by the barbarians in the West, it may be asked how it was that in the East, where the same causes operated, the Empire survived much longer intact and united.' But this is a mistake. The three causal elements which Bury rejects may have interacted with each other, and with still other elements, in such a way as to produce very different results in the West and the East." (Fischer, Historians' Fallacies, p. 179.)
- "A complex cause may have a complex effect (e.g. German militarism, British jingoism, naval arms race, colonial rivalry, economics and nationalistic tensions plus other incalculable factors led to (complex effect) the first World War), as argued by James Joll (1984) in The Origins of the First World War." (Cockcroft and Cockcroft, Persuading People, p. 123.)