The law of requisite variety: Why flexibility and adaptability are essential for success

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I first came across the law of requisite variety almost 20 years ago. Ross Ashby proposed the idea in his 1956 book An Introduction to Cybernetics (see p.202-218), and expanded on it in his paper Requisite variety and its implications for the control of
complex systems. The idea became one of the foundational concepts of the field of Cybernetics.

The law is developed mathematically, using essentially what we would now consider game theory. Ashby states it as:

If the varieties are measured logarithmically, this means that if the varieties of D, R, and actual outcomes are respectively Vd, Vr, and Vo then the minimal value of Vo is Vd – Vr. If now Vd is given, Vo’s minimum can be lessened only by a corresponding increase in Vr. This is the law of requisite variety. What it means is that restriction of the outcomes to the subset that is valued as Good demands a certain variety in R.

To make it a little more accessible, I have restated the Law of Requisite Variety (with a slight conceptual reframing) as:

The only way you can control your destiny is to be more flexible than your environment.

Last week I gave the opening keynote at Thunderhead Innovate, where I explored the changing nature of organizations and the imperatives for effective leadership today.

I used this statement of the Law of Requisite Variety to describe the reality for organizations today. Only those that are able to be as flexible and adaptable as their environment can control their fate. Otherwise they are completely subject to the increasing variety around them.

It is of course a big ask for any organization, particularly a large one, to be have as much variety and flexibility as the world around it. Yet that is the challenge every company and institution faces today.

More on how to achieve that in another post.