International Encyclopedia of Systems and Cybernetics

1) The condition of elements, subsystems or systems which need of their interactions to maintain themselves.

A whole and its parts are also interdependent.

Considering that any concrete system depends on a specific environment and is related to other concrete systems, it can be seen that the notion of interdependence is fundamental in systems hierarchies, and as a base of the concept of meta- (or supra-) system.

2) A situation within such as a "change in one component brings about changes in others" (B. BANATHY, 1973, p.87).

Interdependence is instrumental for autopoiesis, a systemic process in which it is very strongly reciprocal and leads to a closed cycle of reproduction of the components, specific to the system.

3) Relation by which the existence of two or more parts is reciprocally conditioned by these parts.

J.C. LUGAN proposes a classification of different types of interdependences: "linear, circular, dynamic, cybernetic, dialectic, contradictory" (1993, p.117).

Interdependence is a characteristic of complex systems as opposed to composite systems, whose elements remain independent from each other (i.e. interdependent at most in a collective statistical way).

It increases in relation to the number and the types of interrelations between the parts and signals a growing integration and heterogeneity of the system.

Interdependence is also a basic relation between systems (and groups of systems) when significant outputs of the ones become inputs for the others, and reciprocally. Such a situation leads to reciprocal regulation and eventually to integration within a more global system. In such case, a new internal organization supersedes former intersystemic relations and we are back to organizational closure and autopoiesis.

Interdependence is a very basic feature in systems, starting with their very emergence from formerly untelated elements.

Such a relationship implies continuous or intermittent functional interactions between the elements.

Reciprocity of the interactions tends to derive toward different possible situations:

- one element may manage the other or others in a simple hierarchical way, either through a natural regulation or by the use of a controlling artefact.

- one element may react to some action of the other through a feedback, that can be reiterative or merely occasional, and also be triggered only if some critical value is attained

- when the interactions become generalized and more or less permanent, the elements may tend to become part of a system of higher level

- different kinds of associations become possible, from still more or less lose intermittent connection to commensalism, symbiosis or parasitism.

Interdependence role is obvious at all levels of nature's organization, from subnuclear physics to the man-planet system presently in the making.