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As is well known, in order for there to be a proper
coordination of actions to perception the system must be able to select the
correct choice. The ability of the system to avoid incorrect or
unviable choices is a constraint on the behavior of the control system. If
no such constraint existed, the system would have to try out actions
blindly, and the larger the variety of perturbations, the smaller the
probability that those actions would turn out to be adequate.
Thus all viable modeling and aniticipatory control requires an intermediate
quantity of variety: enough to satisfy the LRV that it is possible to
represent all necessary control systems; but not too much to violate the
Law of Requisite Constraint and leave the system with insufficient
"knowledge" about its environment.
This intermediary balance between freedom and constraint in viable systems
has long been noted in information theory \cite{ZWM84a}. This can be
measured in the intermediate entropy values that can be measured in symbol
systems such as linguistic texts and chromosomes.
