The paper considers work by Gardner and Ashby on the relationship between the connectivity of large systems and their stability, which suggests that all large complex dynamic systems will have a critical level of connectance beyond which they will go suddenly unstable. Further evidence by May on ecological systems supports this view. Reliability in systems, that is maintenance of stability of critical values over long periods of time, is held by Ashby to flow from such systems not being fully joined or connected. It is suggested that these considerations must apply also to attempts to plan and control the future of socioeconomic systems, both in relation to the planned system itself, and to the planning system which tries to invoke requisite variety to control the planned system. Stable systems in planning are thus seen as small, probably subsystemic in nature, not fully-joined, and hence hierarchical in structure. ‘Central’ planning results in instability because of size and complexity of control systems needed, and ‘equality’ is not a sustainable concept, as it requires or implies full connectedness. Finally, three kinds of system situations are put forward as representing gradations of stability and thus of ‘plannability’ or design possibility. These situations tend to show the limits of the plannable.
Modeling and Control of Complex Dynamic Systems: Applied Mathematical Aspects