1. Different problems need different responses
Imagine playing a game in which attacks come from several directions. If your only move is to block the front, you will struggle when an attack comes from behind. You need responses that match the challenges you face.
This illustrates the Law of Requisite Variety, explained by W. Ross Ashby in An Introduction to Cybernetics (1956). Its familiar expression is “only variety can destroy variety”. In simple terms, a system needs enough effective responses to handle the disturbances that could push it beyond acceptable limits.
“Variety” means the range of possible situations or responses. The aim is to keep what matters within safe or acceptable limits, even as circumstances change. One effective safeguard may handle several disturbances, so we do not always need a separate solution for every possible problem.
2. How this relates to cybernetics
Cybernetics studies control and communication in living organisms and machines. Ashby presents it as a way to understand how systems regulate their behaviour (Ashby, 1956, Section 1/1). These ideas also provide a useful way to examine organisations.
A thermostat is a familiar example. It measures the temperature, compares it with a target and adjusts the heating. The next measurement provides feedback on whether the adjustment worked.
An organisation can follow a similar process. It collects information about a problem, takes action and checks the result. If the problem remains, it adjusts its response.
The Law of Requisite Variety sets a limit on what regulation can achieve. Information helps us identify the problem, but we also need suitable responses. A thermostat that controls only heating cannot actively cool a room during hot weather.
For management, this means connecting information, action and feedback with the capacity to respond. Ashby explicitly links a regulator’s capacity to its capacity as a communication channel (1956, Section 11/11, p. 211).
3. The theory in a formula
In Section 11/7, printed page 207, Ashby states that outcome variety cannot be less than disturbance variety minus regulator variety. Expressing his statement as an inequality, with parentheses replacing his subscripts for easy display on a blog:
V(O) ≥ V(D) − V(R)
• V(O): variety remaining in the outcomes.
• V(D): variety of disturbances or challenges.
• V(R): variety of regulator responses.
All three are measured logarithmically. For example, V = log₂(N), where N is the number of distinguishable possibilities. Ashby uses subscripts: V with O, D or R below it. The parentheses here preserve the meaning while allowing ordinary text display.
The meaning is simple: the range of responses limits how far we can reduce variation in outcomes. Under the basic model’s assumptions, achieving one fixed outcome requires V(R) ≥ V(D). Enough response variety is necessary, but the responses must also be selected and applied correctly (Ashby, 1956, Sections 11/7 and 11/11).
Ashby extends the model in Section 11/9, page 209, to account for a system that itself limits the effect of disturbances. A consistent explanatory reformulation is:
V(O) ≥ V(D) − V(R) − K
Here, K represents the reduction allowed by the extended model. Passive protection is a practical interpretation of this term. This equation restates the extension using logarithmic variety throughout; it is not a verbatim reproduction of Ashby’s notation.
The management implication is to strengthen both effective responses and preventive safeguards. These quantities are theoretical measures, rather than scores obtained by counting complaints and staff.
4. One approach cannot solve everything
Consider a university. Students may struggle because of financial difficulties, academic problems, poor accommodation or emotional distress. A general reminder to work harder will not address all these situations.
Financial difficulties may require assistance. Academic problems may need tutoring. Accommodation problems require maintenance or additional capacity. Emotional distress may require counselling and support.
The management lesson is clear: first understand the problem, then choose a response that fits. Follow up to find out whether the response helped. This completes the feedback process.
5. Build capacity across the organisation
A practical implication is that leaders should build the organisation’s ability to respond through its people and systems.
Staff need the skills, information and authority to handle problems within their responsibilities. Clear arrangements for referring difficult cases help them recognise when additional support is needed.
For example, a broken classroom projector should have a clear route to repair. Requiring the head of the organisation to approve every routine repair can delay a straightforward solution. Leadership can focus on recurring failures, replacement budgets and service quality.
6. Prevent problems and use good information
Ashby also distinguishes between responding actively and a system itself limiting the effect of disturbances (1956, Sections 11/9 and 11/11). A warm coat protects against a range of cold conditions without requiring a new action each time the temperature changes.
In an organisation, preventive maintenance and clear procedures can serve a similar purpose. They can reduce the problems that require individual attention.
When a response is needed, information matters. A complaint system is more useful when it records the issue, assigns responsibility and tracks progress. The person who reported the issue should be able to confirm whether it has been resolved. A growing list of unresolved complaints should prompt a review of resources, procedures or authority.
7. Keep learning as conditions change
The Law of Requisite Variety offers a useful question for management: do we have enough effective ways to respond to the challenges we face?
An organisation may need stronger safeguards, better information, additional expertise or more authority at the point where problems arise. The answer will depend on the situation.
As challenges change, our capacity to respond must develop with them. Good management requires us to notice those changes and adjust our systems in time.
8. Reference
Ashby, W. R. (1956). An introduction to cybernetics. Chapman & Hall. https://ashby.info/Ashby-Introduction-to-Cybernetics.pdf