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Problemistics - Problémistique - Problemistica
The Art & Craft of Problem Dealing
Variety
Definition (Stafford Beer)
Definition (George Chadwick)
Definition (Union of International Associations)
Related concept : information (W. Ross Ashby)
Law of Requisite Variety (W. Ross Ashby)
Law of Requisite Variety (George Chadwick)
Law of Requisite Variety (Stafford Beer)
[1967, Second Edition] Stafford Beer, Cybernetics and Management, The English Universities Press, London
“Variety is a suitably descriptive name for the number of distinct elements in the system.” (p. 43)
[1971] George Chadwick, A Systems View of Planning, Pergamon Press, Oxford
“Variety is simply the number of distinguishable elements within a set.” (p. 49)
[1986, Second Edition] Union of International Associations eds., Encyclopaedia of World Problems and Human Potential, K. G. Saur, München
Variety. “The quality or state of differing in kind, consisting of dissimilar constituents or parts that may not be unified or compatible, having different values, opinions, or backgrounds.
1. The quality or state of having numerous forms or types. An intermixture or succession of different things, forms, or qualities. A multiplicity of things within the same class or category that can be distinguished, often by marked differences.
2. The variety of anything is its number of distinguishable elements.
Every conceptual step which enriches the nature of a system under study increases the information about it, increases the uncertainty informing it, and proliferates its variety.
3. The total number of possible states of a system, or of an element of a system.”
(KC0606)
[1956] W. Ross Ashby, An Introduction to Cybernetics. Chapman & Hall, London
“... the concept of ‘variety’, a concept inseparable from that of ‘information’.”
(p. 140)
“Variety (whether information or disturbance) comes to the organism in two forms. There is that which threatens the survival of the gene-pattern - the direct transmission by T (exTernal word) from D (disturbances) to E (essential variables). This part must be blocked at all costs. And there is that which, while it may threaten the gene-pattern, can be transformed (or re-coded) through the regulator R and used to block the effect of the remainder (in T). This information is useful and should (if the regulator can be provided) be made as large as possible; for, by the law of Requisite Variety, the amount of disturbance that reaches the gene-pattern can be diminished only by the amount of information so transmitted. That is the importance of the law in biology.”
(p. 212)
[1956] W. Ross Ashby, An Introduction to Cybernetics. Chapman & Hall, London
"Only variety can destroy variety." (p. 207)
“If, for instance, a press photographer would deal with twenty subjects that are (for exposure and distance) distinct, then his camera must obviously be capable of at least twenty distinct settings if all the negatives are to be brought to a uniform density and sharpness.” (p. 213)
[1971] George Chadwick, A Systems View of Planning, Pergamon Press, Oxford
“The Law of Requisite Variety is the main tool in understanding the ways in which systems can be controlled. The Law is stated simply by W. Ross Ashby (1964): ‘only variety can destroy variety’. In other word, to control a system of given variety we must match it with a controlling system of requisite variety.” (p. 71)
“If a system is to adapt or to control its environment, it must contain at least as much variety as there is in the environment to be controlled.” (p. 72)
[1972] Stafford Beer, Brain of the Firm, Allen Lane The Penguin Press, London
“Ashby’s Law of Requisite Variety, which says that control can be obtained only if the variety of the controller (and in this case of all the parts of the controller) is at least as great as the variety of the situation to be controlled.” (p. 54)