International Encyclopedia of Systems and Cybernetics

"An element or functional component of a larger system which fulfills the conditions of a system in itself, but which also plays a specialized role in the operation of the larger system" (V. CSANYI, 1993, p.67).

According to CSANYI, subsystems are "…communities of simultaneously replicating components".

The subsystem is thus simultaneously an interacting component in a suprasystem and in its own right a system made of interacting components.

This author explains that subsystems result in a progressive way from the increase of specific and different replicative cycles during the process of autogenesis in the recently shaped system: "Their components are separated from others by their participation in co-replication". He adds that: "As time passes, replicative coordination of various supercycles develop and fidelity of replication increases" (1993, p.263) As a result, functional differentiation and cooperation grow on par.

CSANYI's "supercycles" are the primeval form or M. EIGEN's hypercycles, which are thus stabilized supercycles.

A subsystem can in most cases be clearly recognized because it perfoms a specific function.

Subsystems are generally made of numerous components. As a rule, they interact with each other in specific ways. They frequently exchange their products and the output of one of them may be an input for another.

Most of them are critical for the system: the demise of one of them generally brings along the destruction of the whole system within a short time. This is specially true when the system is strongly integrated.

M. BUNGE observes: If a system does have subsystems, not just components, then the cohesion of the subsystems competes with that of the overall system" (1979, p.37). This may explain why, in very complex systems whose global coherence is costly and difficult to maintain, some subsystems may turn more or less parasitic of their own system: Bureaucracy could be an example.