The essential variables E are given, and also given is the set of
states η in which they must be maintained if the organism is to
Survive (or the industrial plant to run satisfactorily). These two
Must be given before all else. Before any regulation can be under-
Taken or even discussed, we must know what is important and
What is wanted. Any particular species has its requirements
Given— the cat must keep itself dry, the fish must keep itself wet.
A servo-mechanism has its aim given by other considerations—
One must keep an incubating room hot, another must keep a refrig-
Erating room cold. Throughout this book it is assumed that outside
Considerations have already determined what is to be the goal, i.e.
what are the acceptable states η. Our concern, within the book, is
Solely with the problem of how to achieve the goal in spite of dis-
Turbances and difficulties.
The disturbances D threaten to drive E outside the set η. If D
Acts through some dynamic system (an environment) T, then the
Diagram of immediate effects is initially
D → T → E
The organism (or whoever is interested in E), however, has some
Power of forming another dynamic system R (e.g. a brain or a ser-
Vomechanism) which can be coupled to T and which, if properly
Made, will form with T a whole, F, so that the diagram of immediate
Effects becomes
D → F → E
219
A N I N T R O D UC T I O N T O C Y B E R NE T I C S
TH E ERR O R- CO N TR O LLED REG U LA TO R
And such that F blocks the flow of variety from D to E, so that E
stays within η.
T is usually given. It is the environment which the organism is
Facing together with those parts of the organism that have to be
Taken as given in the regulation. It cannot just be abolished, but
Can usually be manipulated. The problem of regulation is then, in
General:
Given E, η, T, and D, to form the mechanism R so that R and
T, coupled, act to keep E within η.
From now to the end of the book we shall be studying how var-
ious types of data (E, η, T, and D) can specify the form of
Machine with input (R) that will give regulation. We want to
Deduce the form of R.
Were the situation always as simple as it was in Table 11/3/1,
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The subject would soon be exhausted. As it is, many deviations
From that form are possible, so we shall proceed to examine vari-
Ous deviations, as they put various difficulties in the way of the
Design or specification of the regulator R.
We can now assume, in discussing some particular regulation,
That full use has been made of the possibilities of redefining (S.11/
So that the formulation is either like that of S.11/3, which gave
Perfect regulation and control, or like those in S.11/4, in which
Such perfection was impossible. The remainder of the book will
Be concerned essentially with those cases in which perfect regula-
Tion is not possible but in which we wish the regulation to be as
Good as is possible in the conditions given.
Sensory and motor restriction. A simple introduction to the
Real difficulties is that given when R’s capacity, as a channel for
Transmitting variety or information from D to T, becomes insuffi-
Cient, according to the law of Requisite Variety, to reduce the vari-
ety in E to that in η. When this happens, the regulation is necessarily
Imperfect.
Examples of the phenomenon are myriad. First are all the cases
Of sensory restriction, of deafness, of the driver who cannot see
Clearly through a rain-obscured windscreen. There are the organ-
Isms that cannot see ultra-violet light, and the tabetic who cannot
Feel where his feet are. These are restrictions in the channel from
D to R.
Then there are the restrictions in the channel from R to T, those
On the effector side of R. There is the man who has lost an arm,
The insect that cannot fly, the salivary gland that cannot secrete,
And the rudder that is stuck.
220
A similar restriction of R’s capacity may occur in those cases
Where R’s effect on T is vectorial, i.e. effected through more than
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One channel or component to T, and some diminution has
Occurred in the number of T’s parameters accessible to R. (Com-
Pare S.7/12.) Thus a failure at one of the controls on the dashboard
May impair the driver’s ability to keep the car running well.
The case when R cannot receive full information about T’s ini-
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