The concept of "systems" is widely used in the natural and social sciences and especially in various complex technologies. Possibly it was Jack Burnham, an artist and writer, who first suggested the term (not to be confused with 'systematic') for the visual arts. By its use, he was trying to distinguish certain three-dimensional situations which, misleadingly, have been labelled as "sculpture".
A system is most generally defined as a grouping of elements subject to a common plan and purpose. These elements or components interact so as to arrive at a joint goal. To separate the elements would be to destroy the system. Outside the context of the whole, the elements serve no function. Naturally these prerequisites are also true of every good painting, sculpture, building or similarly complex but static visual entity. The original use of the term in the natural sciences is valuable for understanding the behaviours of physically interdependent processes. It explained phenomena of constant change, recycling and equilibrium. Therefore, I believe there are sound reasons for reserving the term "system" for certain non-static "sculptures", since only in this category does a transfer of energy, material or information occur.
Painters, and sculptors of static works, are anxious to prevent their works from being influenced by time and environmental conditions. Patina is not looked for as a record of the bronzes' response to atmospheric exposure nor is the darkening and crackle of paintings desirable in order to demonstrate their reaction to environmental conditions. Although physical changes take place, the intention of these artists is to make something that alters as little as possible. Equally, the viewer hopes to see the work as it appeared immediately after its execution.
Works, however, have been produced with the explicit intention of having their components physically communicate with each other and the whole communicate physically with the environment. It is this type of work which cannot be classified as "sculpture", whereas it can be described appropriately as a "system".
The physical self-sufficiency of such a system has a decisive effect on the viewer's relationship to the work, due to its hitherto unknown independence from his mental involvement. His role might be reduced to being the source of physical energy in works conceived for viewer participation. In these, his actions -- pulling, pushing, turning, etc. -- are part of the programme. Or his mere presence might be sufficient. However, there are systems which function properly even when the viewer is not present at all, i.e., their programme operates absolutely independently of any contribution on the part of the viewer.
Whether the viewer's physical participation is required or not, the system's programme is not affected by his knowledge, past experience, the mechanics of perceptual psychology, his emotions or degree of involvement. In the past, a sculpture or painting had meaning only at the grace of the viewer. His projections into a piece of marble or a canvas with particular configurations provided the programme and made them significant. Without his emotional and intellectual reactions, the material remained nothing but stone and fabric. The system's programme, on the other hand, is absolutely independent of the viewer's mental participation. It remains autonomous -- aloof from the viewer. As a tree's programme is not touched by the emotions of lovers in its shadow, so the system's programme is untouched by the viewer's feelings and thoughts. The viewer becomes a witness rather than a resounding instrument striving for empathy.
Naturally, also a system releases a gulf of subjective projections in the viewer. These projections, however, can be measured relative to the system's actual programme. Compared to traditional sculpture, it has become a partner of the viewer rather than being subjected to his whims. A system is not imagined; it is real.