Systems Thinking Part 2 — Stocks, Flows, and Feedback Loops

Imagine a bathtub. We don’t typically think of a bathtub as being a system, but it is. Using what we learned in part one, we know a bathtub’s elements are the faucet, the tub, and the drain. These elements are connected by the flow of water. And the purpose of a bathtub is to hold water, so people can clean themselves.

In addition to elements, interconnections, and goals, when describing a system like a bathtub, systems thinkers use three other critical concepts — “stocks”, “flows”, and “feedback loops.” Once you understand all six of these terms, you’ll be a systems thinking master!

Stocks and Flows

As Donella Meadows observes in Thinking in Systems, “A stock is the foundation of any system. Stocks are the elements in the system that you can see, feel, count, or measure at any given time. A system stock is just what it sounds like: a store, a quantity, an accumulation of material or information that has built up over time. It may be the water in a bathtub, a population, the books in a bookstore, the wood in a tree, the money in the bank, your own self-confidence. A stock does not have to be physical. Your reserve of good will for others or your supply of hope that the world can be better are both stocks.”

Stocks are impacted by flows. Flows are what goes into and comes out of systems. “Flows are filling and draining, births and deaths, purchases and sales, growth and decay, deposits and withdrawals, successes and failures…