Illinois, 60680, U.S.A.
and W. Ross Ashby
Biological Computers Laboratory, University of Illinois, Urbana, Illinois 61801,
The design of a complex regulator often includes the making of a model of the system to be regulated. The making of such a model has hitherto been regarded as optional, as merely one of many possible ways.
m this paper a theorem is presented which shows, under very broad conditions, that any regulator that is maximally both successful and simplemust be isomorphic with the system being regulated. (The exact assumptions are given.) Making a model is thus necessary.
The theorem has the interesting corollary that the living brain, so far as it is to be successful and efficient as a regulator for survival,mus t proceed, in learning, by the formation of a model (or models) of its environment.
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