Jay Wright Forrester

"No plea about inadequacy of our understanding of the decision-making processes can excuse us from estimating decision making criteria. To omit a decision point is to deny its presence – a mistake of far greater magnitude than any errors in our best estimate of the process."

"In complex systems cause and effect are often not closely related in either time or space. The structure of a complex system is not a simple feedback loop where one system state dominates the behavior. The complex system has a multiplicity of interacting feedback loops. Its internal rates of flow are controlled by nonlinear relationships. The complex system is of high order, meaning that there are many system states (or levels). It usually contains positive-feedback loops describing growth processes as well as negative, goal-seeking loops. In the complex system the cause of a difficulty may lie far back in time from the symptoms, or in a completely different and remote part of the system. In fact, causes are usually found, not in prior events, but in the structure and policies of the system."

"In spite of the tentative nature of the world model described here, various conclusions are drawn from it. Man acts at all times on the models he has available. Mental images are models. We are now using those mental models as a basis for action. Anyone who proposes a policy, law, or course of action is doing so on the basis of the model in which he, at that time, has the greatest confidence. Having defined with care the model contained herein, and having examined its dynamic behavior and implications, I have greater confidence in this world system model than in others that I now have available. Therefore, this is the model I should use for recommending actions. Those others who find this model more persuasive than the one they are now using presumably will wish to employ it until a better model becomes available."

"It is to be hoped that those who believe they already have some different model that is more valid will present it in the same explicit detail, so that its assumptions and consequences can be examined and compared. To reject this model because of its shortcomings without offering concrete and tangible alternatives would be equivalent to asking that time be stopped. But the world will continue to turn. We always use the most acceptable model at any point in time. But how should we proceed so that the most acceptable model is also the best one that is available? We should try for three things. First, the best existing model should be identified at each point in time. Second, the best currently existing model should be used in preference to traditional models that may be less clear and less correct. Third, aggressive effort should be devoted to a continual improvement in the available models of the world system."

"There may be no realistic hope of the present underdeveloped countries reaching the standard of living demonstrated by the present industrialized nations. The pollution and natural-resource load placed on the world environmental system by each person in an advanced country is probably 20 to 50 times greater than the load now generated by a person in an underdeveloped country. With 4 times as many people in the underdeveloped countries as in the present developed countries, their rising to the economic level that has been set as a standard by the industrialized nations could mean an increase of 10 times in the natural-resource and pollution load on the world environment. Noting the destruction that has already occurred on land, in the air, and especially in the oceans, capability appears not to exist for handling such a rise in standard of living. In fact, the present disparity between the developed and underdeveloped nations may be equalized as much by a decline in the developed countries as by an improvement in the underdeveloped countries."

"In concept a feedback system is a closed system. Its dynamic behavior arises within its internal structure. Any action which is essential to the behavior of the mode being investigated must be included inside the system boundary."

"[The engineer] must identify the significant and critical problems, but in his education, problems have been predetermined and assigned. He must develop the judgment to know what solutions to problems are possible, but in school the problems encountered are known to have answers. He should be excited by new and unsolved challenges, but for 20 years he has lived in an educational system where he knows he is repeating the work of last years students."

"Formulating a model of a system should start from the question “Where is the boundary, that encompasses the smallest number of components, within which the dynamic behavior under study is generated?”"

"The strongest criticism has come from some economists. The objections range from simple misunderstanding, through belief that essential structures have been omitted from the world model, to concern over the costs and feasibility of halting economic growth. Although there is a basis for the criticisms, they have not had sufficient substance to dismiss the central issues. The debate seems to be gradually moving away from the question of whether or not industrial growth must slow to the question of what strategy should be used to limit growth. The latter question, however, remains unanswered."

"It seems traditional for explicit models of social systems to be greeted by vague criticisms about their lack of perfection. Instead, we need equally explicit alternatives with a demonstration that the alternative leads to a different and more plausible set of conclusions. By proposal and counter proposition our understanding of social systems can advance."

"Another tradition in systems theory, known as system dynamics, originated at Massachusetts Institute of Technology. The founder of this tradition was Jay Forrester, a creative engineer who invented the magnetic core memory for computers and who built the , which is now in the Smithsonian Institution."