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Requisite Variety

Defines Requisite Variety, law of requisite variety, Ashby's law

Requisite variety is a principle formulated by W. Ross Ashby in An Introduction to Cybernetics (1956) [cite:@ashby_IntroductionCybernetics_1956]. The law states that a system can only remain stable if it possesses enough internal complexity to match the complexity of its environment. Put formally: a controller can regulate a system only if the controller’s variety — its range of possible responses — is at least equal to the variety of disturbances the system faces.

This has consequences for governance and organizational design. A centralized authority with a narrow response repertoire cannot regulate a complex environment no matter how well-informed it is. Effective regulation requires distributed variety — multiple agents, at multiple scales, with overlapping but distinct response capacities.

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Cites
  • An introduction to cybernetics
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@misc{emsenn2026-requisite-variety,
  author    = {emsenn},
  title     = {Requisite Variety},
  year      = {2026},
  url       = {https://emsenn.net/library/information/domains/cybernetics/terms/requisite-variety/},
  publisher = {emsenn.net},
  license   = {CC BY-SA 4.0}
}