# Ashby's Law of Requisite Variety by John Naughton > “W. Ross Ashby was a British cybernetician working in the 1950s who became interested in the phenomenon of homeostasis—the way in which complex systems operating in changing environments succeed in maintaining critical variables (for example, internal body temperature in biological systems) within tightly-defined limits. Ashby came up with the concept of variety as a measurement of the number of possible states of a system. His "Law" of Requisite Variety stated that for a system to be stable, the number of states that its control mechanism is capable of attaining (its variety) must be greater than or equal to the number of states in the system being controlled.” > **— John Naughton**, *2017, Edge Annual Question, “What Scientific Term Or Concept Ought To Be More Widely Known?”* ## Sources and Context - **Direct Edge response and surrounding essay:** [Ashby's Law of Requisite Variety](https://www.edge.org/response-detail/27150) — Edge published this exact passage in its 2017 Annual Question collection, *WHAT SCIENTIFIC TERM OR CONCEPT OUGHT TO BE MORE WIDELY KNOWN?*. The response page preserves the surrounding argument and qualifications. - **Complete local collection index:** [[research/Edge 2017 Full Quotation Curation|Edge 2017 Full Quotation Curation]] — retained source-first record for the complete response cohort and this passage's promotion status. ## Related Articles and Collections - **Collection:** [[collections/Edge|Edge]] - **Collection:** [[collections/Machine Succession|Machine Succession]] - **Article:** [[articles/The Evolutionary Roots of Silicon Valley|Valley Roots]] - **Article:** [[articles/Modern Artificial Intelligence in the 1970s|AI in the 1970s]] - **Article:** [[articles/Cyber-Physical Lessons from Imperial Beekeeping|Cyber-Physical Beekeeping]] - **Article:** [[articles/STEVE|STEVE]] - **Wiki map:** [[wiki/Cybernetics|Cybernetics]] ## Related Topics - [[wiki/Cybernetics|Cybernetics]] - [[wiki/Second-Order Cybernetics|Second-Order Cybernetics]] - [[wiki/Cybernetic Feedback Loop|Cybernetic Feedback Loop]] - [[wiki/Cybernetic Control|Cybernetic Control]] ## Share on Social Media ``` “W. Ross Ashby was a British cybernetician working in the 1950s who became interested in the phenomenon of homeostasis—the way in which complex systems operating in changing environments succeed in maintaining critical variables (for example, internal body temperature in biological systems) within tightly-defined limits. Ashby came up with the concept of variety as a measurement of the number of possible states of a system. His "Law" of Requisite Variety stated that for a system to be stable, the number of states that its control mechanism is capable of attaining (its variety) must be greater than or equal to the number of states in the system being controlled.” — John Naughton, 2017, Edge Annual Question, “What Scientific Term Or Concept Ought To Be More Widely Known?” https://bryantmcgill.com/simple-reminders-john-naughton-ashby-s-law-requisite-variety ```