W. Ross Ashby

Ashby kept a journal for over 44 years in which he recorded his ideas about new theories. He started May 1928, when he was medical student at St. Bartholomew's Hospital in London. Over the years, he wrote down a series of 25 volumes totaling 7,189 pages. In 2003, these journals were given to The British Library, London, and in 2008, they were made available online as The W. Ross Ashby Digital Archive.[7] Ashby initially considered his theorizing a private hobby, and his later decision to begin publishing his work caused him some distress. He wrote:

My fear is now that I may become conspicuous, for a book of mine is in the press. For this sort of success I have no liking. My ambitions are vague—someday to produce something faultless.[1]^: 97

Ashby found writing so difficult that he took correspondence courses in "Effective English and Personal Efficiency" to prepare to write his first book.[4]

Ashby was interested in mechanistic explanations for adaptive behavior, especially in the brain. By 1941, he had developed a coherent theory and written a 197-page booklet, titled "The Origin of Adaptation".[1]^: 99 This hand-written monograph was made publicly available in January 2021.[8] In it, he expressed his opinion that "there is an abstract science of organisation, in the sense that there are laws, theories and discoveries to be made about organisation as such without asking what it is that is organised."[8]^: 35

In 1948 Ashby built a machine, the homeostat, to demonstrate his theories.[1]^: 98 The machine used a simple mechanical process to return to equilibrium states after disturbances at its input. Earlier, in 1946, Alan Turing had written a letter[9] to Ashby suggesting that Ashby use Turing's Automatic Computing Engine (ACE) for his experiments instead of building a special machine. Norbert Wiener, describing the appearance of purposeful behavior in the Homeostat's random search for equilibrium, called it "one of the great philosophical contributions of the present day".[10] Ashby's first book, Design for a Brain, was published in 1952 and recapitulated this line of research.

Ashby was one of the original members of the Ratio Club, a small informal dining club of young psychologists, physiologists, mathematicians and engineers who met to discuss issues in cybernetics. The club was founded in 1949 by the neurologist John Bates and continued to meet until 1958.

The title of his book An Introduction to Cybernetics popularised the usage of the term 'cybernetics' to refer to self-regulating systems, originally coined by Norbert Wiener in Cybernetics. The book gave accounts of homeostasis, adaptation, memory and foresight in living organisms in Ashby's determinist, mechanist terms.[2]

Ashby's 1964 paper Constraint Analysis of Many-Dimensional Relations began the study of reconstructability analysis, a multivariate systems modeling methodology based on set theory and information theory, which would later be developed by Klaus Krippendorff, George Klir, and others.[11][3]^{: 287–288}

In 1970, Ashby collaborated on simulation experiments regarding the stability of large interconnected systems.[12] This work inspired Robert May's studies of stability and complexity in model ecosystems.[13]

In An Introduction to Cybernetics, Ashby used set cardinality, or variety, as a measure of information. With this he formulated his Law of Requisite Variety. Mathematically, the law is a statement about how "in a two-person game the variety possible is determined by the number of possible choices open to the two players".[14] When regulation is seen as a game between a regulator ${\displaystyle R}$ and source of disturbances ${\displaystyle D}$, "only variety in ${\displaystyle R}$ can force down the variety due to ${\displaystyle D}$; only variety can destroy variety."[15]^: 207

In work with Ashby, Conant augmented this with the "Good Regulator theorem" stating that "every good regulator of a system must be a model of that system".[16] Stafford Beer applied the law of variety to the practice of management, founding management cybernetics and developing the Viable System Model.[17]

A popular paraphrasing of the law is "only complexity absorbs complexity". However, while a web search reveals many attributions to Ashby, it appears such attribution is in error. The phrase is not listed by the Cybernetics Society.[18]