by Hugh M. Lewis

The lack of a basic, general definition of a "system" serves as a critical short-coming in the development of systems-based perspectives, models and applications. 

General Systems Definition:

A system is a finite co-occurring set of event structures that form subsystem components, that are relationally self-organizing between components, and that exhibit mutual constraint such that the relations occurring between them tend to be minimally non-random and recurring within a developmental sequence, and such that the system as a whole exhibits thereby integrative properties of emergence, negentropic growth of order, dynamic-state equilibrium and self-perpetuation under varying sets of external conditions.

In general, a system is any self-integrated pattern that maintains regular order, in some minimal sense, against a general meta-systems gradient or encompassing set of tendencies towards disorder.

At this time, I distinguish three general types of systems, depending upon the degree of non-random constraint that governs their integrative patterns, and that determines the ontological and developmental status of the component subsystems.

Type 1 systems: Internally integrated systems. These are usually the most determined of systems, with highly constrained relations and interactions, and exhibit the most non-random of patterns. If any component parts from such a system that are critical to the functioning of the system are removed, then the system as a whole cannot be sufficiently maintained. The component parts of such systems cannot be maintained outside of the internalized context that the system as a whole provides, and would end when the system ends. Type 1 systems tend to be highly differentiated internally in a functional and structural sense, such that component subsystems tend to take on highly compartmentalized and specialized functions.

Type 2 systems: Externally integrated systems. These are usually only partially determined and with less constraint governing the relationships occurring between the parts. In such contexts it is usually the case that individual component parts of the system may be removed from the system, and the system will maintain its equilibrium without significant disturbance. It is also often the case that individual component parts can be self-maintaining outside of the context provided by the larger system. The basis for the organization of such Type 2 systems seems to be the intervention and condition of external constraints that are tied to the shared meta-systems context or environment in which they subsystems exist. Type 2 systems may be said to be less differentiated than type 1 systems, such that component parts may be to some extent interchangeable, and functional articulation of the subsystems substitutable by alternate components.

Type 3 systems: Heterogeneous systems. These are mixed self-organizing systems that by definition are usually the least constrained and determined, the least enduring and tend to be the most ephemeral. Such systems often involve interactions and regular relationships between component parts across levels or orders of integration of natural reality, or across extensive boundaries of other systems. It is the case in such systems that the component parts are probably parts of other Type 2 systems simultaneously as being involved in a Type 3 system, and such components can be fully self-maintaining independent of the meta-systems context provided by the Type 3 system. Type 3 systems seem to exhibit the most chaos of pattern in their state-path trajectory and are therefore the most open and subject to the perturbation of external influences.

Though we define general systems by a common set of definitions, we must also limit our general definition by stating that, though all real systems may be defined generally as a system, each specific system is unique in terms of its overall patterning and complexity in relation the meta-systems context in which it occurs. Our definitions apply in only a general or non-specific sense, and the understanding of any particular system requires that we specify its unique event pattern.

It makes sense therefore to distinguish what we can call "general systems" or  a single case of "a general system" from what may be referred to as specific or "particular systems" as in "this particular system." All real systems may be said to be both a particular system, and at the same time, a general system of a particular type, kind or level of integration.

The distinction between general systems and a particular system is an important analytical and semantic difference to draw upon in the definition of systems. We must be careful to specify a particular system or kind of system in the statements we make about a system, and to separate those features unique or characteristic of that system or kind of system, from any other systems, or from the general properties or patterns that can be ascribed to all systems. A general systems model and definition provides us a point of entry into the examination and comprehension of any particular system or kind of system, but it is not the final set of statements we want to arrive at about any given set or set of systems.

General Systems Essays, Vol. I