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Requisite Variety

"Only variety can destroy variety."  ::  Ross Ashby

Ashby's Law of Requisite Variety is a central law for the proper functioning of every mechanical and biological entity. It has, over the years since it was first propounded, been totally ignored by social scientists and their patrons, the administration of the day, because it represents a refutation of the need for the concentration of power in central government as the only way to solve problems (or generally to deal with reality) in a complex society.
In fact, the law supports the exact opposite view, declaring, with the support of logical reasoning and empirical evidence, that only variety can master variety, reducing disturbances and promoting harmonious order.
Regulation is possible only if the regulating system is as various and flexible (responsive to changes) as the system to be regulated. 

This principle disposes of the myth (still cherished by journalists and sociologists in search of easy popularity) that extraordinarily complex situations demand the concentration of extraordinary powers in a central entity. Once we get rid of that myth we are ready to explore all the rich implications of the Law of Requisite Variety as we advance  towards finding a real solution for the (supposedly) intractable problems of contemporary life.

The passages above have been taken from Ross Ashby's book 'An Introduction to Cybernetics'  published by Wiley(1956). Chapter 11 particularly refers.



In creating computer programmes you need a model. Models are provided by our brains and these models are inevitably massive variety attenuators. This is because they select only those aspects of the world that are relevant to their model’s purpose. Further the models adopted are not the best that we can provide: they are consensual models based on a particuler sets of beliefs. Beliefs are of very low variety. One way of attenuating variety in an ICT project is to ignore it by failing to consult end-users - either intentionally to keep a project 'uncluttered' so that code cutting can start, or simply to avoid undue contact with other 'people', notably thoes who in fact have the relevant know-how.