Having studied several specific systems in some detail, it is now worth considering systems and their properties in general. This will provide a firm foundation for the results of Chapter 5, and at the same time, suggest further directions in which techniques for analyzing nonquantifiable phenomena have been and can be developed.

Of the various approaches to the notion of system, that associated with the name of Mesarovic is most confluent with the viewpoint expressed here. Without any formal structure in mind, Mesarovic thinks of a system simply as a relation on abstract sets. To analyze particular problems, however, structure must be added – but only that necessary for the given purpose. This is the approach adopted below. After an initial presentation of the general definition of system, the specific systems of Chapter 5 are derived as special cases. Next various forms of systemic causality are examined. Subsequent considerations relate to connections between systems, feedback, and the problem of control. The chapter concludes with a classification scheme for systems based on the theory of categories. Because the discussion is primarily definitional and provides little in the way of formal proof, the reader who is interested in rigorous argument may wish to refer to Mesarovic and Takahara.