International Encyclopedia of Systems and Cybernetics

"… (a system that) has the property that if displaced from a state of equilibrium and released, the subsequent movement is so matched to the initial displacement that the system is brought back to the state of equilibrium" (W.R. ASHBY, 1960, p.54).

Such property could be considered as a generalization of the Principle of LE CHATELIER.

ASHBY emits a series of interesting comments related to the properties of the stable system.

He writes: "A variety of disturbances will therefore evoke a variety of matched reactions"… and "… the behavior of a stable system may be described as "goal seeking" (Ibid).

Furthermore "An important feature of a system's stability (or instability) is that it is a property of the whole system and can be assigned to no part of it."

Or, in other words: "The stability belongs only to the combination; it cannot be related to the parts considered separately" (Ibid, p.56).

This implies that no change can be introduced in some specific part of the system without triggering some side effects and, possibly a complete reordering of the whole system, or even its destruction.

ASHBY expresses the same idea as follows: "In a stable system the effect of fixing a variable may be to render the remainder unstable" … and"… the presence of stability always implies some coordination of the actions between the parts".

The stable system, as a model, corresponds also to PRIGOGINE's concept of the thermodynamic system near of its point of equilibrium, i.e. not submitted to giant fluctuations that could transform it radically or destroy it.

Stable systems are also called "Equilibrium Systems", in opposition to critical systems. P. BAK expresses their stability condition as follows: "… under very restrictive conditions, equilibrium systems can exhibit scale-free behavior" (1996, p.35). This seems to be equivalent to PRIGOGINE's concept stated in his theorem of minimum entropy production.