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Ashby's Law of Requisite Variety


  • Variety, with regards to cybernetics, is simply a descriptor of the number of possible states within a system.
  • For example, a light switch has a variety of 2 (on and off), whilst a single die has a variety of 6 (1, 2, 3, 4, 5, 6).
  • The number of states of variety depends on what can be sensed by the observer/the context (e.g. infinitesimal changes of light by a dimming switch may not be detected).

Variety grows exponentially with the size of organisations and major systems, creating vast amounts of complexity with regards to its interactions. Some real-world systems have levels of variety which are effectively infinite. However, our perceptions attenuate ('filter-out') any variety which is irrelevant to what we are trying to observe.

Variety Attenuators

Attenuators within human beings are formed by our physiology and by social conditioning, and similar processes/bases for attenuation exist within organisations. However, these business attenuators often filter out information which can be crucial to operation, thus being damaging to the success and effectiveness of organisations. 

Variety Amplifiers

Similarly, we often attempt to increase our own production of variety as an adaptive strategy to deal with high levels of variety intruding from our environment. The obvious example within humans is our brains - millions of neurons, synaptic connections and subsequent systems which create innumerable combinations and levels of variety. Within humans, the complexity of our brains and their systems created a repertoire of strategies and capabilities which could deal with unexpected variety produced by all kinds of environment. 

Ashby's Law

W. Ross Ashby was a British cyberneticist and psychologist who, during the 1960s, proposed a law with regards to levels of variety and regulation within biological systems. In his words: 

When the variety or complexity of the environment exceeds the capacity of a system (natural or artificial) the environment will dominate and ultimately destroy that system.

This law, now well-known as the First Law of Cybernetics, can also be described as: 

In order to deal properly with the diversity of problems the world throws at you, you need to have a repertoire of responses which are (at least) as nuanced as the problems you face.

Or, even more simply:

Variety absorbs variety.

Systems/organisms must have a number of control mechanisms or responses which are at least equal to, or greater than, the number of potential disturbances/challenges that the systems must face.

Though this law was originally devised with regards to how organisms are able to (and are forced to) adapt to their environments, it was quickly adapted relative to Claude Shannon's information theorem, and systems in general. These ideas were built upon later by Stafford Beer with regards to organisational/societal control and managerial structures.

Example: some writers have suggested that a winning sports team (e.g. football) can be described as operating with more variety than the losing team.

Though the losing team's defence may have practised and developed many systems for defending, the other team's attacking strategies proved too varied and resulted in them scoring more goals.

Strategy and Flexibility

For organisations and teams, Ashby's law effectively means that they must always remain more flexible with their approaches to strategy and operation than the levels of structure and complexity within their systems and operating environment. 

Sometimes this variety is small, but sometimes it can be large, and therefore it is up to the organisations, teams, and the leaders within them to assess the appropriateness of their current systems for the environment they operate in.

The focus is often on efficiency within organisational structures, rather than on the variety needed to survive, adapt and thrive on innovation. 

Standardisation does work well when the variety the organisation is exposed to is known and limited (e.g. repetitive production of the same goods or products within the organisational core) but not when it is unknown, or unlimited (e.g. project management groups, innovation departments, or the police). Standardisation - such as producing a fixed range of products - works by reducing the levels of variety available. However, the complexity of other operating environments, particularly in the digital age, means that this is no longer feasible.

Teams and organisations which face high quantities of unknown and far-reaching variety must develop systems which allow them to respond to external stimuli and challenges beyond the individual capacity of their members and processes. Systems and subsystems responsible for innovation, or managing change/variety should be adept at absorbing information (e.g. new market information, new strategies, inventions) and forming new strategies and services themselves.

Information flow and communication are also extremely important when developing hierarchies and structures which can respond to many different stimuli, as differing flows of information and new combinations of processes create unique responses and actions (recursion). This communication can be through channels internally within the organisation and with external individuals, associates and consultants who offer greater flexibility and variety in response. The variety of stimuli being received should, in theory, be able to be dealt with by different combinations of the system's hierarchy.

Formal strategies and approaches are often useful as references and systems in response to certain stimuli, especially those which are often repeated in similar forms. However, they are not necessarily useful when the environment is particularly variable and the organisation or team often finds itself faced with new and challenging scenarios.

The more variable the operational environment, the more flexible the organisation and its internal systems need to be.

Suggested Reading

  • Ashby, W.R. (1956). An Introduction to Cybernetics. Chapman & Hall.
  • Ashby, W.R. (1963). An introduction to Cybernetics . London.
  • Conant, R. (1981). Mechanisms of Intelligence: Ross Ashby's papers and writings . Intersystems Publications.