View source for Requisite Variety

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== 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 ==
* [[Cybernetics]]
* [[Complexity Theory]]
* [[W. Ross Ashby]]
* [[Adaptive Systems]]
* [[Feedback Loops]]

== References ==
* Ashby, W. Ross. '''An Introduction to Cybernetics'''. Chapman & Hall, 1956. [(http://www.rossashby.info/)
* Beer, Stafford. '''Brain of the Firm'''. Wiley, 1972. [https://www.wiley.com/en-us/Brain+of+the+Firm-p-9780471948391](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. [https://www.springer.com/gp/book/9783642191098](https://www.springer.com/gp/book/9783642191098)

[[Category:Cybernetics]]
[[Category:Systems Theory]]
[[Category:Complex Systems]]
[[Category:Adaptive Systems]]