p.207 the variety in outcomes, if minimal, can be decreased
further only by a corresponding increase in that of R... This is the law of Requisite Variety. To put it more picturesquely:
only variety in R can force down the variety due to D; variety can destroy variety.
This thesis is so fundamental in the general theory of regulation that I shall give some further
illustrations
p.209 the law of Requisite Variety enables us to apply a measure
to regulation.
p.211 The law of Requisite Variety says that R's capacity as a
regulator cannot exceed R's capacity as a channel of communication.
In the form just given, the law of Requisite Variety
can be shown in exact relation to Shannon's Theorem 10, which says that if noise appears in a message, the amount of noise
that can be removed by a correction channel is limited to the amount of information that can be carried by that channel.
Thus, his "noise" corresponds to our "disturbance", his "correction
channel" to our "regulator R", and his "message of entropy H" becomes, in our case, a message of entropy zero, for it is constancy
that is to be "transmitted". Thus use of a regulator to achieve homeostasis and the use of a correction channel to suppress
noise are homologous.
p.213 The formulations given in this chapter have already suggested that regulation and control are intimately
related.
p.214 perfect regulation of the outcome by R makes possible a complete
control over the outcome by C... The achievement of control may thus depend necessarily on the achievement
of regulation. The two are thus intimately related.
p.215 In our treatment of regulation the emphasis has fallen on its property of reducing the variety in
the outcome; without regulation the variety is large - with regulation it is small.
p.241 the inborn characteristics of living organisms are simply the strategies
that have been found satisfactory over centuries of competition, and built into the young animal so as to be ready for use
at the first demand.
p.243 If the reader feels that these studies are somewhat abstract
and devoid of applications, he should reflect on the fact that the theories of games and cybernetics are simply the
foundations of the theory of How to get your Own Way.
p.244 Regulation in biological systems certainly raises difficult
problems... What is usually the main cause of difficulty is the variety in the disturbances that must be regulated against.
p.245 It now follows that when the system T is very large and the regulator R very much smaller
(a common case in biology), the law of Requisite Variety is likely to play a dominating part. Its importance is that,
if R is fixed in its channel capacity, the law places an absolute limit to the amount of regulation (or control) that
can be achieved by R, no matter how R is re-arranged internally, or how great the opportunity in T... the quantity
of control that he can exert is still bounded.
p.245 before Shannon's work it was thought that any channel, with a little more skill, could be modified
to carry a little more information. He showed that the engineer's duty is to get reasonably near the maximum, for beyond it
no-one can go. The law of Requisite Variety enforces a similar strategy on the would-be regulator and controller: he should
try to get near his maximum - beyond that he cannot go.
p.247 Let us then consider the question of what constraints may occur in the disturbances that affect
very large systems, and how they may be turned to use. The question is of major practical importance, for if
R's capacity is not easily increased and the other methods are not possible, then the law
of Requisite Variety says that the discovery of a constraint is the would-be regulator's only hope.
p.248 So many of the well-known regulations are repetitive that it is difficult to find a regulation that
acts only once.
p.249 In the case when the individual disturbances each threaten the organism with death, Good in
the Grand Outcome must naturally correspond to "good in every one of the individual outcomes".
p.251 we must now start to consider how a regulatory machine is actually to be designed and made.
