LAW OF REQUISITE VARIETY

(1) the amount of appropriate selection that can be performed is limited by the amount of information available. (2) for appropriate regulation the variety in the regulator must be equal to or greater than the variety in the system being regulated. Or, the greater the variety within a system, the greater its ability to reduce variety in its environment through regulation. Only variety (in the regulator) can destroy variety (in the system being regulated). The law was formulated by Ross Ashby. (Umpleby)

Its two interpretations are: (1) The amount of appropriate selection that can be performed is limited by the amount of information available. More information might be wasted but less information results in arbitrary decisions (see chance). (2) To confine the variety in system with input, the regulator (see regulation) of that system must have at least as much variety available as the variety disturbing the system through its inputs. "Only variety (in the regulator) can destroy variety (in the system being regulated)" (Ashby). The LAW OF REQuired model-regulator identity is a more general version of the law of requisite variety. (Krippendorff)

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