Ashby's Law of Requisite Variety
Updated 2026-08-16
INTRODUCTION
English translation pending.
CORE DEFINITION
W. Ross Ashby formulated the law of requisite variety in his work on cybernetics: for a regulator to hold a system within a set of acceptable states, the regulator's variety must be at least as great as the variety of disturbances acting on the system. The core claim is that control is limited by the number of distinct responses available, not by the strength of any single response. The qualification is that the law speaks of variety rather than power, so a controller can satisfy it either by adding responses or by reducing the variety it must absorb.
SCAFFOLDING EFFECT
Reduce cognitive load
- Disturbance inventory: count the distinct kinds of disruption the system must absorb. - Response design: check that your control has at least as many distinct responses as disturbances. - Variety reduction: cut the variety reaching the controller through standardization, buffering, or filtering.
Anchor fast decisions
Every distinct disturbance requires a distinct corrective response if it is to be neutralized, so a controller with fewer responses than disturbances cannot prevent some of them from propagating. The mismatch is not a matter of effort: applying the wrong response more forcefully does not reduce the variety that escapes. Control therefore improves either by enlarging the response repertoire or by filtering the disturbances before they arrive.
MINIMUM ACTION
In progress 0/1Practice this model in one real situation:
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Source support: Explicit
- en.wikipedia.orghttps://en.wikipedia.org/wiki/Variety_(cyberneticsverified
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