Here are a few descriptive efforts targeting the question "what's a system?":
"The word 'system' is used today with the same meaning it had originally in Greek. A system is a group, or collection for which there is some unifying principle -- a "standing together." Even in ancient times it often referred to collections which moved together, e. g., the planetary system or musical harmonies."
W. McWhinney (1991, Systems Theory Program notes c/o The Fielding Institute)
"Although ... the word 'system' has been defined in many ways, all definers will agree that a system is a set of parts coordinated to accomplish a set of goals."
C. West Churchman (1968, p.29)
"A system is a set of elements that cannot be separated into independent parts. From this it follows that (a) the essential properties of a system are lost when it is disassembled physically or conceptually, and (b) the essential properties are also lost when the parts are separated physically or conceptually from the whole."
R. L. Ackoff (1981, p.245)
Here are a few quotes (from more well-known scientists) relevant to the question "what's a system?" that focus on the value of relationships and viewing the whole:
"Today the network of relationships linking the human race to itself and to the rest of the biosphere is so complex that all aspects affect all others to an extraordinary degree. Someone should be studying the whole system, however crudely that has to be done, because no gluing together of partial studies of a complex nonlinear system can give a good idea of the behavoir of the whole."
Murray Gell-Mann
"Matter at each level of complexity appears to consist of two interdependent, nonidentical elements in dynamic interaction and in integral relation to each other. It appears that an interacting, dynamic, asymmetrical binary relationship is the fundamental module of order in the cosmos. I have the impression that the interactions in these dynmamic asymmetrical binary systems underlie all phenomena in nature ... The most fundamental phenomena in the universe is relationship. It then becomes possible to recognize the underlying unity in all the diversity of the phenomena of life."
Jonas Salk
"A human being is part of the Whole ... He (She) experiences himself (herself), his (her) thoughts and feelings, as something separated from the rest ... a kind of optical delusion of his (her) consciousness. This delusion is a kind of prison for us, restricting us to our personal desires and to affection for a few persons nearest us. Our task must be to free ourselves from this prison by widening our circle of compassion to embrace all living creatures and the whole of nature in its beauty. Nobody is able to achieve this completely, but the striving for such achievement is, in itself, a part of the liberation and a foundation for inner security."
Albert Einstein
(With special thanks to the folks at: www.newciv.org/ISSS_Primer/seminar.html for these quotes from Gell-Mann, Salk and Einstein. Also, please note editorial liberty taken to include 'she, herself and her' in Einstein's quote to ensure a greater feeling of inclusion for female ecosystem scholars.)
Here are two scholarly quotes focused on systems thinking and systems philosophy, respectively:
"Systems thinking: An epistemology which, when applied to human activity is based upon the four basic ideas: emergence, hierarchy, communication and control as characteristics of systems. When applied to natural or designed systems the crucial characteristic is the emergent properties of the whole."
P. Checkland (1981, p. 318)
"In contrast to the reductionist, deterministic and uni-directional cause-and-effect thinking of classical science, systems philosophy brings forth a reorganization of ways of thinking. It creates a new worldview, a new paradigm of perception and explanation, which is manifested in integration, holistic-thinking, purpose-seeking, mutual causality and process-focused inquiry."
B. Banathy Sr. (1991, p. 31 & 32)
Here's a succinct satire depicting the danger of scholars ignoring the whole system and failing to appreciate the value of the relationships among its various parts.
"THE RAISIN BREAD CULTURE: A Fable for Ferment"
By Arnold Schultz September 1970
This is the story of a civilization known as the Raisin Bread Culture. Its world was loaves of Raisin Bread.
Through the centuries scholars devoted their lives to the study of Raisin Bread. They invented dissecting instruments. They separated the raisins, the nuts, the cinnamon, and the baked dough. They brought these separate elements of the world into their laboratories where each would be studied analytically and with extreme precision.
Great institutions were established to teach what the scholars had learned. These institutions of learning came to be known as polyversities. Four discrete and highly respected disciplines arose: Raisinology, Nut Science, Cinnamonics, and Pastronomy. The disciplines came to be housed and nurtured in separate departments of the Great Polyversities. These departments, named after the disciplines, produced experts of world renown. In academic circles, the raisinologist was most revered -- the reason: the raisin could not be reduced. But in spite of the Raisinologist's high status, specialists from other disciplines did not often talk to him. They didn't understand his language.
By and by, all the bread began to get mouldy and sour and bad to eat. The people looked to their Great Polyversities for answers as to why this was happening. But the scholars from the high-ranked disciplines were not concerned. The people went to certain of the very best Polyversities and asked, "Why don't you study the whole loaf of bread so that the relations among the nuts, raisins, spices, and dough remain intact?"
"Oh no," said the scholarly experts. "The loaf is much too large and too complex. For us to know the loaf would be like knowing the universe. That's all right for God and philosophers but not for us Nobel-bound scientists."
"Then, at least," argued some of the people, "why don't you cut the loaf into vertical slices? That way, the elements could still be studied together?"
The learned scholars of those very best Polyversities did not listen to that argument. After all, had not their departments just been toasted as the top, scholastically, in the world?
Outside the Polyversities many things were tried. The bakers changed their technology. The government suggested getting used to mouldy bread. Some groups suggested switching to cake. But in spite of everything, the civilization eventually fell -- because the Polyversities would not change. Their scholars felt that, after all, what other culture did they know that in five hundred years had added so much knowledge as had theirs!
With extra special thanks to Arnold and his beloved Ecosystemology Students:
http://www.cnr.berkeley.edu/~schultz/!raisinb.htm