Requisite Variety
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[hide]Definition
Requisite variety is a principle from cybernetics and systems theory that states that a system must possess at least as much complexity as the environment it seeks to control or adapt to. This concept, originally formulated by British cybernetician W. Ross Ashby in his 1956 book An Introduction to Cybernetics, is often summarized as *"Only variety can absorb variety."* ([ashby.info](http://www.rossashby.info/))
Definition
Requisite variety asserts that in order for a system (biological, social, technological, or organizational) to remain stable and effective, it must have enough internal diversity to respond to the complexity of its external environment. If a system lacks sufficient variety, it risks becoming overwhelmed by unforeseen changes, leading to failure or instability.
Applications
The principle of requisite variety applies to various disciplines, including:
Cybernetics and Systems Theory
- Used in feedback loops and control mechanisms to ensure systems can respond to dynamic environments.
- Essential in designing artificial intelligence and adaptive technologies.
Management and Organizations
- Organizations must be adaptable enough to handle market changes, technological disruptions, and social shifts.
- Decentralized decision-making structures often embody requisite variety by allowing flexibility in problem-solving.
Biology and Ecology
- Ecosystems exhibit requisite variety through biodiversity, which ensures resilience to environmental changes.
- Human immune systems use variety in antibodies to counteract a diverse range of pathogens.
Information Security
- Cybersecurity strategies incorporate requisite variety by continuously adapting to new threats.
- Machine learning models improve robustness by increasing dataset diversity.
Political and Social Systems
- Democracies and resilient societies often allow diverse viewpoints and flexible governance to adapt to changing circumstances.
- Overly rigid or homogenous systems struggle to absorb social complexity, leading to breakdowns.
Related Concepts
- Law of Requisite Variety – Ashby’s formalized principle that states a system’s internal diversity must match or exceed external complexity.
- Self-Regulation – The ability of a system to adjust and stabilize itself based on feedback.
- Homeostasis – The maintenance of equilibrium in biological and social systems through adaptive responses.
- Resilience Engineering – The study of how systems maintain function despite disruptions.
See Also
References
- Ashby, W. Ross. An Introduction to Cybernetics. Chapman & Hall, 1956. [(http://www.rossashby.info/)
- Beer, Stafford. Brain of the Firm. Wiley, 1972. [1](https://www.wiley.com/en-us/Brain+of+the+Firm-p-9780471948391)
- Espejo, Raul. Organizational Systems: Managing Complexity with the Viable System Model. Springer, 2011. [2](https://www.springer.com/gp/book/9783642191098)
