Elements are the most noticeable parts of systems and usually the least important in defining the unique characteristics of the system unless they can change relationships or purpose. Changing relationships usually change system behavior. A system may be dramatically altered if its interconnections are changed.
The most crucial determinant though of a system’s behavior is often its function or purpose despite being the least obvious part of a system. A change in function or purpose can be drastic, changing a system profoundly, even if every element and interconnection in the system remains the same. For myself, this means that if two systems have the same elements but a different set of interconnections between those elements and different purposes then they can be considered distinct systems.
These are, however, all abstract concepts. To deal with changes physically manifested in the world Systems Thinking uses the more ”concrete” concept of stocks. A stock is an accumulation of material or information built up over time and, according to Meadows, is the foundation of any system. Stocks are the elements of the system that can be seen, felt, counted, or measured at any given point in time. A stock, like elements of which stocks are comprised, does not have to be physical.
A system makes a manifested change in the world, whether through physical means, a river turning turbines or intangible, economic uncertainty leading to the election of a right-wing government.
”If you understand the dynamics of stocks and flows—their behavior over time—you understand a good deal about the behavior of complex systems”.
Stocks change over time through the actions of flows, both in and out. “A stock, then, is the present memory of the history of changing flows within a system”. Stocks are therefore not static. Even if in a state of dynamic equilibrium in which the level of a stock does not change, there is a continuous flow through it. This may give the appearance of unchanging permanence.
It is much more difficult to change the level of the stock abruptly than it is to adjust a flow. Stocks, especially large ones, respond only gradually to change, even sudden change. A vital, key point to understanding why systems behave as they do is that “a stock takes time to change, because flows take time to flow”. Stocks usually change slowly, acting as delays, lags, buffers, ballast, making them sources of momentum in a system.
”People often underestimate the inherent momentum of a stock. It takes a long time for populations to grow or stop growing, for wood to accumulate in a forest, for a reservoir to fill up, for a mine to be depleted”.
The presence of stocks allows inflows and outflows to be independent of each other and, moreover, to be temporarily out of balance with each other.
We seem to be more capable of focusing on stocks than on flows and on inflows more than on outflows. Often failing to see that a stock can be increased by decreasing its outflow rate as well as by increasing its inflow rate.
Humans have invented hundreds of stock-maintaining mechanisms through individual and institutional decisions designed to regulate the levels in stocks and to make inflows and outflows both independent and stable. Monitoring stocks constantly, making decisions to take actions designed to raise or lower stocks or to keep them within acceptable ranges. Those decisions, along with the mechanisms for regulating the levels in the stocks by manipulating flows, add to a collection of “feedback processes.
"Systems of information-feedback control are fundamental to all life and human endeavor, from the slow pace of biological evolution to the launching of the latest space satellite. . . . Everything we do as individuals, as an industry, or as a society is done in the context of an information-feedback system".
—Jay W. Forrester
Feedback mechanisms are then a mechanism that operates through a feedback loop to create consistent behavior that persists over time. Feedback loops can cause stocks to maintain their level within a range or grow or decline. Flows into or out of a stock are adjusted based on changes in the size of the stock itself. Whoever or whatever is monitoring the stock’s level begins a corrective process, adjusting rates of inflow or outflow (or both) and so changes the stock’s level. The stock level feeds back through a chain of signals (information) and actions (physical changes) to control itself.
A feedback loop is then formed when changes in a stock affect the flows into or out of that same stock. A bank interest-bearing savings account is a simple and direct feedback loop. The total amount of money in the account (the stock) affects the amount of money coming into the account as interest (the flow) based on earning a certain percent interest each year. The total amount of interest paid into the account each year (the flow in) is not a fixed amount, but varies depending on the size of the total amount in the account (stock) and increases the stock amount by that much for the next iteration.
The stock is adjusted by the flows into or out because of changes in the size of the stock itself. A corrective process is taken then by whoever or whatever is monitoring the stock’s level, adjusting rates of inflow or outflow (or both) and thereby changing the stock’s level. The stock level feeds back through a chain of signals (information) and actions to control itself.
- As long as the sum of all outflows exceeds the sum of all inflows, the level of the stock will fall.
- As long as the sum of all inflows exceeds the sum of all outflows, the level of the stock will rise.
- If the sum of all outflows equals the sum of all inflows, the stock level will not change; it will be held in dynamic equilibrium at whatever level it happened to be when the two sets of flows became equal.
Not all systems have feedback loops. Some systems are relatively simple open-ended chains of stocks and flows. They still have elements, interconnections and function or purpose and might be affected by outside factors, but the levels of the systems own stocks wouldn't affect its own flows.
If the feedback mechanism tries to keep a stock at a given value or within a range of values through a stabilizing, goal-seeking, regulating loop it is called a balancing feedback loop.
”A balancing feedback loop opposes whatever direction of change is imposed on the system. If you push a stock too far up, a balancing loop will try to pull it back down. If you shove it too far down, a balancing loop will try to bring it back up”.
The idea being that if one knows all the dynamic possibilities of say a simple bathtub model one could deduce several important principles that can be usefully extended to more complicated systems.
Systems can also have an appropriate time horizon to the system question or problem being investigated allowing one to question what came before, and what might happen next. This helps to understand trends of system behavior over time instead of focusing too much attention on individual, (and all too often immediate) events. Behavior-over-time graphs can help with determining if a system is approaching a goal or a limit, and how quickly.
Whether elements or stocks, they are still models that we create of the real world. All models, whether mental models or mathematical models are still simplifications of that real world, subject t0 the often quoted George Box aphorism, “All models are wrong, some models are useful”.
Meadow also speaks of leaders in control of a system being able to, “play a different game with new rules, or can direct the play toward a new purpose”. However, she also says that (because stocks can be), “long-lived, slowly changing, physical elements of the system, there is a limit to the rate at which any leader can turn the direction of a nation”. So they too often make empty promises, changes that fail and blame the other side.
“Changes in stocks (by a country) set the pace of the dynamics of systems. Industrialization cannot proceed faster than the rate at which factories and machines can be constructed and the rate at which human beings can be educated to run and maintain them”.
While time lags coming from slowly changing stocks can cause problems in systems, they also can be sources of stability. “If you have a sense of the rates of change of stocks, you don’t expect things to happen faster than they can happen. You don’t give up too soon”.
This sense cannot, however, be held by only a few. Our existing entrenched systems make it too easy to choose leaders that really don’t have our best interests in mind even if well-meaning in their hearts. In this use “our” is meant to be applied as expansively and inclusively as possible. The question then is can democratic processes be applied in using Systems Thinking? The answer suggested by Systems Practice and from New Community Paradigms so far seems to be yes.
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