On Growth

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34. Jay W. Forrester

Professor Forrester teaches at the Alfred P. Sloan School of Management at the Massachusetts Institute of Technology in Cambridge, Massachusetts.
Jay W. Forrester was born in Anselmo, Nebraska, in 1918. He majored in education. In 1940 he cofounded the servomechanisms laboratory at MIT. He founded the Digital Computer Laboratory there and became professor at the Alfred P. Sloan School of Management. He has written extensively on digital computers and the dynamics of economic behavior. A team basing its research on the work of Forrester, led by Dennis L. Meadows, prepared the by now world famous Limits to Growth report for the Club of Rome, published in 1972.
A complete list of Professor Forrester's work is produced as an appendix to this conversation.

Professor Skinner¹ complained that ninety percent of the reviews of his book, Beyond Freedom and Dignity, were based on misunderstanding or on an unwillingness to face the issues he raised. Perhaps the mental models through which people perceived his book were inappropriate. How have the reactions been to your World Dynamics and The Limits to Growth by Meadows?²

I feel much the same. In fact, after reading the reviews of Skinner's book, I saw such a similarity to the reviews of World Dynamics and The Limits to Growth that I was sure it would be necessary to read his book even to determine the central message. When faced with a book that violates the conventional wisdom or that uses an unfamiliar methodology, a reviewer often distorts a book or even reverses its meaning. The nature of the reviewing process must be understood in this connection. Those with negative reactions rush into print much more quickly than those with positive reactions. Furthermore, a reviewer usually feels an obligation to differ with an author; otherwise he would not seem to

1 See conversation no. 7.

2 See bibliography, conversation no. 34.

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be making an intellectual input himself. I think in the reactions to World Dynamics and The Limits to Growth we will see the same trends that occurred with the earlier system-dynamics books. The first reviews are negative. Then thoughtful people interested in the subject begin to dig more deeply and to examine the issues. After the first rush of negative reviews, a very different tone begins to develop. Even in the very short history of these two recent books, a change in reaction is occurring.

How would you describe system dynamics, which is the methodology behind the two books? Where has system dynamics come from?

We have been developing system dynamics at MIT since 1956. It arises from the confluence of three earlier lines of endeavor - the classical or descriptive approach to social systems, the theory of feedback structures and dynamic behavior, and the development of computers.

The first background thread, the descriptive approach to social behavior, underlies the liberal arts and the classical approach to education. It is the method of the historian and social commentator - to report, evaluate, and predict. In its most formal manifestation the classical method of description and verbal analysis appears in the case-study approach to education as used in schools of law and medicine and as popularized by the Harvard Business School in the case-study method of management education. This classical tradition, which uses description, analysis, argument, and intuitive judgment, is now the basis for all political decisions, for the passing of all laws, and for the making of all management decisions.

The classical decision-making procedure has great strengths, but also great weaknesses. Its strength arises from the direct human observation of forces, pressures, and reactions within our social systems. Each person has a rich store of information from observing men and institutions. Each person filters his observations through discussion of pressures, human reactions, and assumed consequences. Each has a rich body of acquired knowledge on the separate facets and components of social systems. For the most part these observations are correct at the elementary level of the individual pressures and responses in the system.

But the classical approach to social systems has two serious weaknesses: As one weakness, the classical tradition gives little guidance in separating the important information from a tremendous body of irrelevant information; as another weakness, the classical tradition supplies no methodology for interrelating and interlinking a given set of assump-

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tions and arriving with certainty at the consequences implied by the assumptions.

So, the classical process of managing social systems has available a tremendous store of valid information about the parts of the system, but no adequate way to select the significant information from the excess of information, and no way to be certain of the consequences that follow from selected information about individual pressures and human reactions. Consequently, the classical tradition subjects people to information overloading and to a high degree of internal contradiction because different people draw different conclusions from the same input facts. Often the accepted conclusions are inconsistent with the accepted assumptions and these discrepancies go undetected because the systems are so complex that the human mind is unable to properly relate the multiplicity of causes to the wide variety of possible consequences.

The second thread forming the background of system dynamics has been under formal theoretical development for a hundred years. I refer to a field that is variously called cybernetics, or servomechanisms, or feedback-system theory. Feedback theory deals with closed-loop behavior in which a control action (decision) alters the state of a system (the levels in system dynamics) and sets up new information conditions for the guidance of future decisions. Every decision, whether public or private, whether conscious or unconscious, is made in the context of such a feedback-loop structure. All the processes of growth, goal-seeking, equilibrium, oscillation, and decay are generated by the interplay of forces within feedback loops.

The first professional paper on feedback dynamics of which I am aware was presented in 1867 before the Royal Society in London by Clerk Maxwell, better known for his discovery of Maxwell's equations for the propagation of radio waves through space. His paper, ‘On Governors,’ presented a mathematical analysis of the stability and behavior of the fly-ball governor as used on James Watt's steam engines. The Bell Telephone Laboratories revived and extended feedback theory in the development of feedback amplifiers for use in transcontinental telephony. During World War II the concepts were refined and applied to military equipment. More recently, extensions of the theory have guided the design of chemical plants, oil refineries, and control systems for aircraft and space satellites. We have continued the development of the principles as they apply to very nonlinear, multiple-loop systems containing both positive and negative feedback.

The principles that emerge from feedback theory guide the sorting and

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the organizing of the information that is available from the classical tradition of direct observation of real life. The principles from feedback theory tell us what items of information from the morass of direct observations might be relevant in producing a given observed mode of real-life behavior. The feedback system principles become a screen for separating important data from the useless. Furthermore, the system principles provide a guide to how the selected information is to be structured into an interactive system. The principles of structure and behavior from feedback theory help us escape from the information overload that is inherent in the classical traditions of descriptive analysis. But one would still be left with more information and with greater structural complexity than the human mind can handle.

The third background development, the high-speed electronic computer, solves the problem of how to draw correct dynamic conclusions from a given set of assumptions. The computer is given a simulation model, which is a statement of the motivational assumptions and information flows for each point in the system and a specification of how the forces interact at each local point in the system. The computer then simulates, or traces through step-by-step, what will happen as the separate elements of the system impinge on one another.

So, from the classical tradition comes too much information, from the feedback theory comes guidance for sorting and structuring that information, and from the development of computers comes the ability to analyze the consequences of structured observations about social systems.

In a television interview, Dr. Djhermen M. Gvishiani³ of the Soviet Union indicated to me that the significance of computers has been exaggerated, that we must take sociological and psychological aspects into consideration and these cannot be represented in computers.

I agree that the press and many others overemphasize the computer aspect of our work. The most important input to a system dynamics model is the descriptive information and our perceptions about the influences and responses at different points in a social system. The second major conceptual input comes from the feedback-system principles that allow one to select from the excess of descriptive information and to organize the relationships that have been chosen. The computer is necessary as an economical tool but is not a part of the conceptual or theoretical structure of system dynamics.

My only disagreement with Dr. Gvishiani would be if he thinks that

3 Vice Chairman of the State Committee of the USSR Council of Ministers for Science and Technology and corresponding member of the USSR Academy of Sciences.

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psychological and sociological aspects cannot be put in a computer-simulation model. One can incorporate any relationships that can be described. Any of the so-called intangibles can be represented in a model. One must establish a scale of measurement (that is arbitrary); he must relate the scale to actual situations; and he must try to be consistent in the way the scale is used. By forcing the past intangibles to become future tangibles, we become more precise. Thought and discussion becomes more orderly and more penetrating. The psychological and sociological aspects of our systems are of overwhelming importance. They can and must be included in formal models.

You speak of social systems as being multi-loop feedback systems. It is not clear what you mean by a closed loop that connects an action to its effect.

A feedback loop exists wherever the surrounding state of the system determines action that affects the system state. This is an absolutely sweeping definition that encompasses everything that changes through time. One can structure the dynamics of a simple swinging pendulum as a feedback process in which the position of the pendulum determines acceleration that determines velocity that determines position. One can examine the processes of evolution as continuous adjustment between a species and its environment in which biological change alters the suitability of the species to its circumstances and sets up new pressures for favoring those members of the species that fit best. Management and political decisions are made in the context of a feedback structure where the decisions are intended to change the surrounding socioeconomic circumstances and the changed circumstances present an ensemble of new information that becomes the basis for future decisions.

But the closed-loop viewpoint is in sharp contrast to the way most people think of cause-and-effect relationships. Most people see not the whole circular process, but only a unidirectional fragment of the entire process. Ordinary discussions and debates focus on how action A will cause result R, without continuing into a consideration of how result R will lead to a new pattern of action A. Most articles in the public press also focus on the simple unidirectional viewpoint and obscure the true circular dynamic structure that is causing social change.

Perhaps a simple example will help. If one fills a water glass from a faucet, he usually thinks of the flow of water as filling the glass, and the description stops at that unidirectional stage without identifying the

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remainder of the closed-loop causal structure. But it is equally true that the water in the glass is turning off the faucet. The person watches the water and closes the faucet as the proper water level is reached. The entire system is one in which the flow of water fills the glass but, just as correctly, the water in the glass controls the flow.

The process is circular and closed-loop; action alters the state of the system and the new state modifies the action. All dynamic behavior is generated by these closed-feedback loops. There are two distinct kinds of feedback loops: Positive feedback loops produce all the processes of growth; negative feedback loops produce goal-seeking, equilibrium, and fluctuation.

Several people interviewed for this book have said, ‘We don't need computers to deal with such matters.’

In one sense that is true; in another and much more important sense it is entirely untrue. It would be fair to say that we have never discovered anything in fifteen years of analyzing social systems that someone could not honestly say he already knew and had already stated. But on every major issue there is a split opinion. People take each side of every question. On important issues, the division of opinion is apt to be in the forty percent to sixty percent range, with no assurance that the majority will prove to be right. But with such controversy, it is almost impossible to imagine coming up with an answer that has never been articulated before. The confusion arises because for each correct statement, there has been someone, whose credentials are just as good, who has claimed the opposite.

When the controversy over sheer use of computer simulation models is resolved, we will find that formal models reduce the controversy over the substance of the social issues. The reduction of controversy will take place at two levels. First, the method forces a focus on the underlying assumptions without simultaneous consideration of the implied consequences of those assumptions. The basic assumptions must be faced in their own right, without involving a prejudgment of whether or not they will lead to the desired conclusions. In the classical method of political debate, assumptions and consequences are hopelessly intertwined. One tends to start with an outcome to which he is committed and then to argue for a set of assumptions about present circumstances that appear to lead to the desired outcome. Separate assumptions are not explicitly stated and are not individually debated to resolve differences of opinion.

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Usually, when assumptions are explicitly stated, as they must be in a computer model, much of the disagreement evaporates. Often it is only, lack of clarity and semantic difficulties that lie behind the argument.

At the second level, the classical procedure of debate produces endless disagreement over what consequences would occur in the future from an accepted set of present assumptions. This level of conflict can be entirely eliminated between those who accept the system-dynamics methods because there is no doubt about the computer producing the consequences of the assumptions and relationships given to it.

During my interviews on the subject of The Limits to Growth I was surprised that people in certain disciplines - I am thinking of economics - who should be working on the same kind of planetary models as you, would show reluctance to enter into contact with those of you in system dynamics.

You are probably drawing unjustified generalities from a few individuals. Your comment is not typical of all economists. Our work has in the past drawn in relevant people representing many kinds of viewpoints. The Limits to Growth work was in very broad contact with many kinds of people in many different disciplines to provide information inputs to the various aspects of our work. I am now myself beginning a new program that will deal with social and economic change at the national level with a particular focus on the United States. It is already evident that we will get excellent cooperation in this from people in all areas of endeavor. Some individuals will avoid contact and participation, but that is not typical of people generally or any profession in particular.

But in my interview with William Nordhaus,⁴ an economist at Yale, he mentioned having written a review of your World Dynamics in which he asserts that your book contains assumptions that are quite contrary to empirical data that is available. Have you read that review?

Yes. The Nordhaus review has not been published, but it has been circulated on a private basis very widely in Europe and North America. The review is an example of the errors and fallacies that can be created by someone who does not understand a new field, but sets himself up as an instant expert. The review alleges three major and three minor errors in World Dynamics. In fact, a careful analysis of the review shows that every point rests on gross error by the reviewer or on his misreading

4 See conversation no. 19.

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the World Dynamics book - things like mistaking a function for its derivative, reading the wrong units of measure for a variable, creating variables that are not in the book and then attributing them to the book, and misusing the real-world data when he brings it to a comparison with superficially similar but quite different concepts in the model. The review shows how poorly a classical, static training in traditional economics prepares a person for understanding the nature and the behavior of nonlinear, multiple-loop feedback structures of which our social systems are composed.

I have written an analysis of and reply to that book review; it is available to anyone that requests it. In fact, my reply shows that the data presented by the reviewer strongly support the assumptions in World Dynamics when the errors in the review are corrected.

One criticism of World Dynamics has been that resources should have been measured in economic and not in physical terms and that the model is misleading because it does not include a pricing system.

Those who suggest that the solution to shortage lies in the price system are speaking from a short-term view and are thinking about relative and not about absolute shortages. They are probably speaking from the tradition of the economist's profession where everything tends to be converted into money terms before it is discussed. But there is nothing in a pricing mechanism that generates physical space or generates resources that don't already exist in the earth's crust. Pricing is a way of redirecting effort and of determining who uses the remaining short supplies. Those who can afford the high prices will continue to use resources after others who can no longer afford the high prices have been excluded from the market. The price mechanism is by no means a solution to the issues raised in World Dynamics.

Realistic doubts about the significance of the price mechanism are stated by Professor Wallich of Yale in Fortune:⁵ ‘We know, of course, that the prices of most natural resources today do not reflect expectations of future shortages.... We cannot be sure whether, given the prospect of shortages at some future time, the price system would in fact respond with sufficient foresight. Various factors besides human fallibility suggest that it might not.’

He then moves from resources to one of the clearly limited aspects of the environment, namely, land: ‘The economics and politics of land represent a special aspect of the natural-resource problem. Land is

5 October, 1972.

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broadly fixed in supply.... Here again, the price system does not offer complete assurance of being able to take care of the situation.... A good deal of evidence has accumulated that the price system, if not intrinsically inappropriate, is at least substantially inefficient in dealing with regional crowding. It appears that population movement responds to rising rents and rising congestion only with very long time lags.’ Here we see a recognition of the importance of long delays. We see a suggestion that prices, far from generating supply, can only operate to determine who consumes when availability falls short of need.

To put the matter another way, I look upon prices as intermediary variables that determine who shall receive allocations of a short resource. Many people have argued that higher cost will cause people to make use of lower-quality resources and that the process will extend supply by a greater use of capital, energy, and manpower. That is true and the concept is incorporated in my World Dynamics model. It is also incorporated in The Limits to Growth model, not as a price system, but through a physical extraction-efficiency system. One must realize that the falling quality of resources implies a higher effort for extraction and this implies a real, as distinguished from a monetary, inflation. The rising price implies a falling productivity. It means, therefore, a lower standard of living, because it means more effort put into producing the same unit of goods. A great deal more can be done in handling allocations - I don't mean that the treatment has been complete or final, but only that such issues have not been overlooked.

Some people have implied that the growth-and-collapse modes shown in the books occur because price and financial processes are implicit rather than explicit in the highly aggregated models. I believe that the effect of adding prices and financial flows will be in the opposite direction. New modes of system instability will become possible in the model as the additional system levels and interactions are added between money and material. When the full behavior Of the socioeconomic system becomes clear, I believe it will become evident that the price and monetary system is subject to at least as much mismanagement as the physical, demographic, and physical-capital aspects, and that the price and financial flows, rather than insuring a trouble-free transition, introduces additional hazards along the road from growth to equilibrium.

Some readers of World Dynamics feel that growth in technology has been neglected.

That reaction to the book I simply did not anticipate. Otherwise, the

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nature of the handling of technological change could have been more completely explained. It would have seemed to me as quite unlikely, considering the years that I have been involved in science and technology, for people to believe I was not aware of the rapid pace of scientific advancement. The issue is not dealt with in detail in World Dynamics, but it is explicitly stated on page 53: ‘Capital includes buildings, roads and factories. It also includes education and the results of scientific research, for the latter are not represented elsewhere in the model system and the investment in them decays at about the same rate as for physical capital.’

The point here involves the proper use of aggregation of variables into a model of reasonably simple structure. One can aggregate into a single variable those things that have similar dynamic behavior. Research and technological change have a dynamic behavior very much like that of physical capital accumulation. Both have, under circumstances that favor growth, a positive feedback character. Capital produces more capital; knowledge is the basis for producing still more knowledge. Both decay. The major fraction of our technological know-how resides in the heads of people and must be rebuilt in every human generation by an expensive investment in education. The time constants of obsolescence and disappearance of that knowledge are similar to the time constants for physical capital. Furthermore, the significant use of each is the same; knowledge and physical capital both raise the standard of living, increase the efficiency of capital accumulation, and increase the yield of agriculture. These are the three uses of the combined capital-knowledge variable in the World Dynamics model. So, capital and scientific knowledge are aggregated together because they are generated in a similar way, they have a similar life, and they are used for the same purpose.

Several people have criticized the publication of The Limits to Growth book without the prior publication of details of the computer model from which the results were obtained.

That was an unexpected result of funding and organizational difficulties. However, the criticism is only partly justified. First, the draft of The Limits to Growth model was made available in the spring of 1972 at the time of the appearance of the book to several research groups that wanted to examine it in detail, had a group of people to assign to the task, and were equipped with access to a computer to work with the model. Second, the message in The Limits to Growth is essentially that of World Dynamics, and the model details for World Dynamics have been

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available from the first. The rather large book with details and justification of The Limits to Growth model will be out in 1973.

This brings us to the question of values and priorities. Some believe the poor nations will have quite different opinions on growth from the rich nations.

Your question implies that the rich nations would favor the end of exponential growth while the poor nations would not. But there is no unanimity of view in the developed countries, and I believe there will likewise be no single view in the underdeveloped countries. In fact, the terminology may need to be changed from developed and underdeveloped to ‘overextended’ and ‘equilibrium’ countries. The less-developed countries may be better able to sustain their traditional goals and values than are the developed (overextended) countries.

I believe we will see two schools of thought in the less-developed countries. Political leaders who have been educated in the developed countries and who have adopted the academic and political values of the industrialized nations will favor growth until the growth-generated pressures overshadow their future and their political credibility. But the traditionalists and the philosophers in those countries may see that the past values are more in keeping with the long-term future and will favor holding onto the past rather than going in quick succession through two upheavals in values - to growth and back to equilibrium - merely to return to a society more like their own past than like the industrialized pattern.

The less-developed countries may adopt a more rational view than the developed countries - as one reason, they have more time to act. We should be very cautious in jumping to conclusions about how other groups will react; we have discovered in our earlier work that social and political groups respond quite differently from expectations. Sometimes the groups who may appear to be the most immediately and detrimentally affected are the very groups that have the greatest incentive to act wisely for the long run and show the greatest ability to look beyond the short term.

We may find that the assumed dedication of underdeveloped countries to economic growth is largely in the minds of economists, government bureaucrats, and businessmen in the developed countries who have been trying to push their own values and goals onto the less-developed countries. As those growth values are cast into doubt and are shown to

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be of only transient advantage, it is entirely possible that the less-developed countries will turn against those whom they begin to perceive as holding out false hopes and values. Because the economic-growth ethic has not been as pervasively adopted in the underdeveloped as in the developed countries, we may find that the trauma of coming to terms with the future is less severe for the poor countries than for the rich countries.

One of the criticisms of your World Dynamics has been that to move into zero growth would be a destructive solution to our present problems.

Some critics of the recent world studies seem to think that we are recommending the impossible, that we are suggesting that growth can be stopped immediately. Maybe the reaction is based on some of the computer runs that show what would happen if action were taken now. But, of course, major changes in values and in political policies do not occur rapidly. The computer runs are intended to show that even immediate action leads to great stress and that delayed action will lead to greater stress in the world social system. Time is short, but there is still time for choice and time to argue, accept, and implement policies that will be more favorable than continuing as at present.

We face two great dilemmas: Continuation of growth will be more destructive of present human values and institutions than will an expeditious slowing of growth; but to stop growth will create its own set of pressures - less severe than letting growth go unchecked but still substantial. There seem to be no pressure-free utopias in sight, but there are many alternatives from which to choose between possible futures. The challenge is to examine the nature of the alternatives and to choose the set of pressures that will lead us into a viable and sustainable future.

The message from World Dynamics and The Limits to Growth is: Ignoring pressures today will lead to still greater pressures tomorrow. If we take action as soon as possible, those actions may be difficult and may generate short-term controversies and pressures, but such action can reduce the pressures that we will otherwise face in the relatively near future. The issue is not one of evading pressures. Instead, the decision is in terms of which pressures, when, and for what purpose.

Dr. Carl Kaysen⁶ of the Institute for Advanced Study feels that the growth mechanisms lie much deeper in our social order than shown in the models by you and Dennis Meadows.

6 See conversation no. 11.

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The depth perceived in a system-dynamics model is very much a reflection of what the reader wants to see. If he wishes to perceive the least possible content, he arrives at a very different conclusion than if he wants to perceive the greatest possible content. In a highly aggregated model there is bound to be room for differing interpretations. It is possible that the different interpretations are both correct, depending on what the individual is doing with the model. The world models in their present high degree of aggregation do not explicitly show the full detail of psychological and sociological forces that connect physical variables to human responses. The system-dynamics methodology can readily accept the full scope of any psychological, moral, sociological, or value structures that one wants to include. To do so will be important in future modeling of world and national dynamics. But in World Dynamics the desire to focus on only the major intersectoral forces between population, capital, food, resources, and pollution meant that for simplicity many intervening variables like prices and psychological reactions were properly subsumed into the more tangible variables from which they are generated and into which they have their effect.

Have you ever included the more intangible variables in models?

Yes, we know it can be done. One example was a model of the dynamics of corporate growth, only summary descriptions of which have been published. That model incorporated some 250 variables that interact in causing the growth and crises of a new technically based corporation. That corporate model contains the psychological and leadership characteristics of the company founders, generates the way the traditions and history of the organization itself influences goals and objectives, and deals with the sociology and psychology of the corporate resource-allocating process. But such a model is extremely complex and detailed; it lacks the simplicity and clarity necessary in a book like World Dynamics if the model is to be understood by the average reader in the time he has available. Furthermore, we must keep in mind that the mental models now being used for national and world decision-making are probably no more comprehensive than those presented in World Dynamics and The Limits to Growth.

Should the world models be expanded to include social and psychological influences?

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A model of considerably greater complexity is eventually desirable. Partly this will be to verify the adequacy of simpler models; partly the adding of omitted variables will allow the model to generate additional modes of behavior that may be possible in actual social systems. There are additional kinds of stresses and additional modes of population equilibrium and collapse that the simpler models cannot represent. But including the additional variables probably will not change the major message of the two books.

And that message is?...

Present world values and the resulting growth trends in population and industrialization cannot continue for more than a few decades. Many different pressures can reshape the future. Some routes to the future are much more favorable than others. The harder we strive to continue the present policies, the higher will counteracting pressures from the natural and social environment rise. We still have time to make choices that will influence the future. Unlike those who have put a ‘doomsday’ label on the two books, I see them as messages of hope. We can have a better future than that which blind devotion to past values and traditions portends.

But since there is an urgency, can you train sufficient system-dynamics specialists to do the vast amount of research and teaching that are needed?

There is a great urgency, but the training and research will be delayed for a time by the high degree of controversy that now exists around the work and the issues raised. The controversy is probably unavoidable because it is part of a transitional period between a past certainty that the old traditions were satisfactory and the new modes of thought, education, analysis, and social-system design about which you have been asking. At present it is not likely that one could organize the kind of financial support necessary to establish the faculty development needed to create an entirely new educational system from the secondary grades up. I think the doubts will disappear. Then it will be possible to get on with the task. Now is a period we must go through. Any substantial break with past tradition unavoidably produces a controversy while the new ideas become accepted.

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How hopeful are you that this can be achieved in a relatively short time? Could the Chinese or the Soviets be drawn into your approach like the Japanese have been, for instance?

I receive mail and letters from practically every country. The mail from outside the United States totals as much as from inside. The letters bring in questions, comments, requests for speeches, and proposals from people to come here to study from every kind of country, the socialist countries included. There is a very widespread knowledge of what we are doing. The ideas have not yet penetrated deeply but have traveled widely. People everywhere are beginning to think much more actively about systems that affect the future of society.

Looking at responses around the world since the publication of World Dynamics and The Limits to Growth, one finds an enormous amount of discussion of the issues that have been raised. Are you hopeful that the reactions will reach enough people to create a corps of leaders who can analyze the future prospects of mankind and can alter present attitudes and policies?

The issues are so substantial and the new directions must be so different from the old that leadership alone will not be sufficient. There must also be widespread public understanding and support. To achieve such, our educational system must become much more effective in conveying an understanding of how the socioeconomic-technical-environmental system functions. I believe that the concepts imbedded in what we call system dynamics will make that possible.

System dynamics is a way of interrelating, on a common basis, the different intellectual disciplines and the different facets of existence, so that one can put into a single structure the technological, economic, ethical, psychological, political and natural aspects of our existence. One can relate all on a par to one another to see how they interact to produce social and economic change. The problems of the world are not being generated from the issues that lie within any single intellectual discipline or any single subsector of our surroundings. The problems and stresses are being generated by the interactions between the many subsectors. Nowhere in our educational system and nowhere in our political system are these interactions adequately dealt with - not in the United Nations, not in governments, and not in corporations.

A complete revolution in our understanding of the world about us is

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in the offing. This new understanding will be developed on a common foundation of dynamic behavior that can be applied to any field or combination of fields. In this new kind of education a student will focus on structures that reappear in many different fields. There are dynamic structures in physics that reappear in management, politics, and ecology. When a structure and its possible behavior is understood, one understands it whether that structure is found in medicine, or in corporate policy, or in demography. These are ideas the teaching of which can begin at the junior high school level.

The world needs a modern version of the ‘Renaissance man,’ meaning individuals who are able to move between intellectual disciplines, understand each of many fields, and grasp their significant interrelationships. Unnecessarily, educators have abandoned the hope of ever achieving again the kind of man who could penetrate the apparent complexities of the multiple facets of human affairs. But we should not despair of finding a new fundamental foundation underlying the proliferation of academic diversity. That is now in sight. It will be possible to build bridges of common dynamic structures and behavior between the liberal arts, science, biology, and social affairs.

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Bibliography of System Dynamics Publications

Forrester, Jay W. Industrial Dynamics. Cambridge, Mass.: MIT Press, 1961. The first book on system dynamics illustrates use of the methodology through analysis of the problems of an industrial firm.

Forrester, Jay W. Principles of Systems. Cambridge, Mass.: Wright-Allen Press, 1968. Basic introductory text on the philosophy and methodology of system dynamics.

Forrester, Jay W. Urban Dynamics. Cambridge, Mass.: MIT Press, 1969. An application of system dynamics to urban problems.

Forrester, Jay W. World Dynamics. Cambridge, Mass.: Wright-Allen Press, 1971. Presents Professor Forrester's preliminary global model on which the Club of Rome's later research reported in The Limits To Growth is based.

Forrester, Nathan B. The Life Cycle of Economic Development. Cambridge, Mass.: Wright-Allen Press, 1972. Presents a system dynamics model of national economic development.

Meadows and Meadows, ed. Toward Global Equilibrium: Collected Papers. Cambridge, Mass.: Wright-Allen Press, 1973. Collects thirteen papers describing individual research on issues evolving from the Club of Rome's study.

Meadows et al. Dynamics of Growth in a Finite World. Cambridge, Mass.: Wright-Allen Press, forthcoming, 1973. The technical report of the Club of Rome project describing the complete model, purpose, and methodology.

Meadows, Dennis L. Dynamics of Commodity Production Cycles. Cambridge, Mass.: Wright-Allen Press, 1970. Presents a general dynamic model of long-term commodity production cycles.

Meadows et al. The Limits to Growth. New York: Universe Books for Potomac Associates, 1972. The general report of the Club of Rome project describing the exponential growth trends that dominate the global society.