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Requisite Variety (Ashby's Law)

Why It Matters

Sets a lower bound on complexity. Simple rules can't control complex systems. Either increase controller variety or reduce system variety.

The Key Move

Compare the variety in the disturbances/environment with the variety in your control responses. If environment variety exceeds control variety, you will fail to regulate. Solutions: increase control options or reduce environmental variety (standardize inputs).

Classic Application

Customer service scripts. If customers can ask 1000 different questions but agents have 50 scripted responses, many interactions will fail. Either train agents for more variety or constrain what customers can ask.

Surprising Application

Attention and filtering. The world has near-infinite variety. Your attention is finite. You must filter. What you attend to is a choice about which variety to match.

Failure Modes

  • Attempting to control with insufficient variety
  • Ignoring the costs of increasing variety
  • Not distinguishing real variety from noise

Go Deeper

Ashby's "Introduction to Cybernetics." Beer's "Brain of the Firm."