Accordingly, we give hereafter many definitions, obtained from authors of different countries and specializations. As much as possible, they are supported by comments of the authors themselves. In some cases a critical evaluation or comment has been added.

The general idea is to extensively explore the multiple aspects of the notion in a non-contradictory way.

To put things into perspective here is G. WEINBERG’s one: "The system is a point of view". And similarly, for G. PASK it is a "universe of discourse" (predefined by a reference frame) (1961, p. 22-3).

So "System" corresponds to a man-created general conceptual model for coherent, complex and more or less identificable and permanently observed real world entities.

It should however be noted that no "point of view" and no "universe of discourse" on systems could exist without the simultaneous existence of something on which these subtle arts can be practised and which is generally called "concrete system", or perhaps more imprudently "real" system.

As a result, the most simple and synthetical definitions open the way to careless generalizations and simplifications.

The most elaborated can be limitative, for example, be valid only for living systems.

Furthermore there are various degrees of systemic organization, from the least integrated (composite or distributed systems) to the most differentiated and integrated ones.

Shortly, there is no perfect definition... and, again, many possible ones according to the "point of view".

Accordingly, we will thus give a number of them, first general, next more specific, in every case with the needed comments (from authors or from this compiler, according to necessity). Most definitions are from genuine systemists or cyberneticians, and some more from other scientists or philosophers, because they seemed relevant.

In conclusion, a critical synthesis will be proposed, even as the conclusions are by no means to be taken as definitive.

Definitions

-"A system is a set of elements dynamically interacting and organized in relation to a goal" (J. de ROSNAY, 1990, p. 93).

J. de ROSNAY comment is as follows: "The introduction of finality (the goal of the system) in this definition may seem surprising. Understandably, the finality of a machine has been defined and specified by man, but what dare we say about the finality of a system like a cell? the cell’s "goal" is in no way mysterious. It implies no project. It is registered a posteriori to maintain its structure and to divide itself. The same can be said about the ecosystem. Its finality - again, not project . is to maintain its equilibria and to allow life’s development. Nobody did established atmosphere’s content of oxygen, nor the earth’s average temperature, nor the composition of oceans. Nevertheless, they maintain themselves within very narrow limits.

"This definition steps back from another with a certain structuralist overtone, for which a system is a closed structure. Such structure cannot evolve, but undergoes collapses due to some internal desequilibrium" (ibid).

"A set of parts with a common destiny, which maintain their interrelations, even when placed in a different environment" (F.BONSACK, 1990, p. 67).

The author comments: "In a system, there is first an object: a certain connexity in space, a conservation of internal relationsat the time of a displacement entailing a change in the relations with the environment...

"But there is more to it.

"There exists a functional unity. This means, a whole apt to perform some tasks and which needs the functional integrity of all of its parts in order to maintain that capacity...

"...a car (for example) performs correctly its function - which is to guarantee quick, safe and confortable travelling at whatever hour and practically any weather conditions - only if all parts correctly perform their respective function" (p. 67)

"A set of interrelated elements" (BERTALANFFY, 1956 - ACKOFF, 1972).

This sweeping and embracing general definition is thus explained by R.L.ACKOFF: "...a system is an entity which is composed of at least two elements and a relation that holds between each of its elements and at least one other element in the set. Each of a system’s elements is connected to every other element, directly or indirectly. Furthermore, no subset of elements is unrelated to any other subset" (Ibid).

This definition does not allow a clear distinction between logical or formal systems, for example, and dynamic concrete systems. Nor is the role of the observer in any way expressed.

"... any set of variables that ( the observer or experimenter) selects from those available on the real "machine" (W.R. ASHBY, 1960, p. 16).

One very important feature of this definition is the emphasis upon the role of the observer or experimenter, who is supposed to "select" the variables, and whose intervention implies clearly that, in ASHBY’s opinion, any system is a mere constructed model. Of course, some criteria would be needed, in order to avoid radical arbitrariness in the process of selection. A criterion should be, for instance, coherence, in relation to some general types of interconnections presen in all systemic-cybernetic models. One should also note that ASHBY postulates the existence of the real "machine", an object "out there", whichmay very well be differently modelized by different observers.

[her er udeladt alt omkring "machine", ca. 2 sider]

To conclude, systems are most generally characterized by their complexity, their coherence and relative permanence, and their tendency to seek their own survival. These general conditions dominate the whole concept.