Requisite variety is a principle formulated by W. Ross Ashby in An Introduction to Cybernetics (1956) (cite: Ashby, 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.
Related terms
- W. Ross Ashby — originator of the law
- Viable system model — organizational structure built on requisite variety
- Cybernetic feedback — the mechanism through which variety is exercised
- Cybernetics — the broader field