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.
By reducing complexity to more cognitively comfortable levels, analysts not only diminish a problem's apparent difficulty, but also transform it from a technologically unanswerable question to yet another designer-engineering task. Thus the fact that a large percentage of the population is malnourished is transformed from a complex political and economic problem caused by a history of exploitation to the more comfortable and technologically familiar problem of growing food. Moreover, once this transformation has taken place, the technocratic mentality focuses exclusively on the dimensions of the redefined task, to the extent that moral and ethical responsibilities or involvement are minimized or even abrogated.