Systems are composed of a few classes of concepts.

  • Elements: Literal parts of the system, including actors and intangible concepts.
  • Interconnections: The ways in which elements work together. While sometimes a physical flow, this can always be interpteted as a flow of information destined for a decision or action point.
  • Stocks: Measurable stores of physical or intangible stuff-of-concern. This is what constitutes the system’s goals’ foundation.
  • Flows: Activities that adjust the level of a stock.
  • Feedback loops: Reactions to changes in stock, which in turn changes inflow/outflow.


  1. Donella H. Meadows and Diana Wright, Thinking in Systems: A Primer (White River Junction, Vt: Chelsea Green Pub, 2008). (See notes.)