"#Cybernetics might, in fact, be defined as the study of systems that are open to #energy but closed to #information and
control—systems that are “information-tight”."
W. Ross Ashby (1956): An Introduction to Cybernetics, (Chapman & Hall, London): now available electronically.
It's interesting that Ashby never uses the phrase "control system" in the book. For him, it seems, the #observer is also the (potential) #controller.