System Thinking - Parts of a System

  • Stocks: Group of resources or inputs into a system. In a bathtub, the stock is the amount of water in the tub.
  • Flows: Movements between stocks. A bathtub has two flows, the tap into the tub, and the drain letting water out. The amount of water is the result of the interaction between the in-flow and the out-flow.
  • Reinforcing Feedback: Change happen in loops, not lines. These loops are feedback forces that work with the stocks and flows. Reinforcing feedback(growth force) happens when the stocks in a system are increasing. In the bathtub, the growth force is the water coming out of the faucet, increasing the stock of water in the tub.
  • Limiting Factor: Systems will collapse if the growth force runs unchecked. At a certain point, the system hits a limiting factor. In the bathtub example, the limiting factor is the desired level of water in the tub. Limiting factors in a system by looking are
    1. Max Capacity of the stocks
    2. Goals of the actors in the system.
  • Balancing Feedback: Balancing feedback kicks in when system approaches its limiting factors. In a bathtub, its someone turning off the water flow when its full. If there is a goal, there will be forces that are trying to achieve that goal by balancing the system. Systems resist change thru balancing feedback that always tries to return the system to equilibrium.
  • Equilibrium: A balanced system is in equilibrium. There are two types...
    • Static: No change in system - because no inflow or outflow. If the tape is closed and the drain is plugged - no inflow or outflow.
    • Dynamic: No change thru equal inflow and outflow. The water in a tub was filling at the same rate it was draining.
  • Leverage: Forces that attempt to change a system. Different leverages have different efficacy. Some will activate the balancing feedback and lock the system. But with careful examination, you can find leverage points that's dramatic enough that a new balance point is found.