Some have said that Ashby's Law of Requisite Variety is the most
significant concept ever developed in systems science.
When I was a lad, we were taught something called "degrees of freedom".
This referred roughly to the number of independent dimensions in a
physical system. In electrical circuits, it corresponded to the number
of independent loops in a circuit. Connected to it was the concept of
superposition (allied with linear systems), where you could get the
response of the system to multiple inputs, simply by addition of the
responses to each of the inputs singly.
As you might know, Ashby finished his distinguished career at the
University of Illinois, where he was a close associate of Heinz von
Foerster, now retired, who has many delightful stories bout Ashby.
In one of these, von Foerster called Ashby in to tell him that a number
of grad students had come to von Foerster to complain bitterly that what
Ashby was teaching was all obvious.
When told this, Ashby burst into a big smile and said something like this:
"Thank God--that's what I've been trying to accomplish for the last