Requisite variety and its implications for the control of complex systems

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Authors: W.R. Ashby

Publication Year: 1958


Journal: Cybernetics and Systems

Volume: 1

Issue: 2

Categories: Information Management, Organizational Behavior


Recent work on the fundamental processes of regulation in biology (Ashby, 1956) has shown the importance of a certain quantitative relation called the law of requisite variety. After this relation had been found, we appreciated that it was related to a theorem in a world far removed from the biological—that of Shannon on the quantity of noise or error that could be removed through a correction-channel (Shannon and Weaver, 1949; theorem 10). In this paper I propose to show the relationship between the two theorems, and to indicate something of their implications for regulation, in the cybernetic sense, when the system to be regulated is extremely complex. Since the law of requisite variety uses concepts more primitive than those used by entropy,I willstart by giving an account of that law.