This is a somewhat trivial solution, though not to be forgotten as
A possibility.
Another possibility is to increase the scope and power of R, until
R’s capacity is made adequate. This method must obviously never
Be forgotten; but we shall give it no detailed consideration. Let us
Consider more fully the interesting case in which the regulation,
Apparently most difficult or impossible, is actually possible.
246
Constraints. What this means, by the law of Requisite Vari-
Ety, is that the variety in the disturbances D is not really as large
As it seems; in other words, by S.7/8, the disturbances show a con-
Straint.
Thus the case we are led to is the following: D has many com-
Ponents, each of which shows variety. The first estimate of D’s
Variety puts it too high, and we are in danger of deducing (if the
Regulator’s capacity is given) that regulation of E to a certain
Degree is not possible. Further examination of D may, however,
Show that the components are not independent, that constraint
Exists, and that the real variety in D is much lower than the first
Estimate. It may be found that, with R’s capacity given, this
Smaller variety can be regulated against, and full regulation or
Control achieved at E. Thus the discovery of a constraint may con-
Vert “regulation impossible” to “regulation possible”. If R’s
Capacity is fixed, it is the only way.
We are thus led again to the importance and usefulness of dis-
Covering constraints, and to yet another example of the thesis that
When a constraint exists it can be turned to use (S.7/14).
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 impor-
Tance, for if R’s capacity is not easily increased and the other meth-
Ods are not possible, then the law of Requisite Variety says that the
Discovery of a constraint is the would-be regulator’s only hope.
As was said in S.7/10, constraints do not fall into a few sim-
Ply- described classes. Having indicated some of the more inter-
Esting possibilities in Chapter 7, I can only continue to mention
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Those classes that are of peculiar interest to us now. With this brief
Reference I shall pass by a vast subject, that comprises a major part
Of all human activity.
Accordingly we shall study one particular form of constraint. It
Is of great interest in itself, it will illustrate the thesis of the last
Chapter, and it is of considerable practical importance in the reg-
Ulation of the very large system.
RE P ETI T IVE DIS T URB ANC E
Though little reference has been made to the fact in the last
Few chapters, many disturbances (and the corresponding regula-
Tory responses) are repetitive, especially if the system is viewed
Over a long time. The cough reflex is regulatory and useful not
247
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
RE GU LA TI N G TH E V ER Y LA R GE SY STE M
Merely because it removes this particle of dust but because, in a
Lifetime, it removes particles again and again— as many times as
Are necessary. Most of the physiological regulators act again and
Again, as often as is necessary. And the coastal lifeboat saves lives
Not once but again and again. If, in the last few chapters, we have
Spoken of “the regulatory response” in the singular, this is only
Because the single action is typical of the set, not because the set
Necessarily has only one element.
So many of the well-known regulations are repetitive that it is
Difficult to find a regulation that acts once only. A possible exam-
Ple is given by an observatory making plans so as to have every-
Thing ready in case a supernova should occur, an event not likely
To occur twice in the director’s lifetime. Various possibilities
Would have to be considered— in which part of the sky it might
Appear, whether during day or night, the spectral and other pecu-
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Liarities which would determine what particular type of plate and
Filter should be used in photographing it, and so on. In making his
Plans, the director would, in fact, draw up a table like that of S.11/
Showing the uncertainties (D) to be feared, the resources (R)
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