The Language of Systems Thinking: Feedback and Delays

Key ideas#

Detail complexity vs. dynamic complexity#

Senge separates two kinds of complexity:

• Detail complexity: many interacting parts, as in assembling a complex machine or managing stock in a large store. Hard, but not necessarily hard in a systems sense.
• Dynamic complexity: the short-term and long-term effects of an action differ, or local effects are the opposite of system-wide ones.

Systems thinking deals with the second kind, and standard forecasting and planning tools, however sophisticated, tend to miss it. A common mistake is to fight complexity with more complexity: adding variables to a model instead of seeing the pattern of change.

Circles, not lines#

Senge’s signature example is filling a glass of water. It feels like a one-way action, but it is a loop: you compare the desired level with the actual level, adjust the tap, the water flow changes the level, and the gap shrinks. Each element is both cause and effect. The structure drives the behavior.

This also changes how you think about responsibility. In a loop everyone contributes to the problem, though not everyone has the same power to change it. Hunting for a single culprit, or blaming only yourself, is a product of linear thinking.

Three building blocks#

• Reinforcing feedback amplifies change in one direction: growth, or an accelerating decline such as a run on a bank. Where you see growth, a reinforcing loop is at work.
• Balancing feedback pulls the system toward a goal, explicit or hidden: a thermostat, or a habit you cannot shake.
• Delays mean effects show up gradually. They hide the system’s nature and make it look as if a fix worked, or failed, when the real effect has not arrived yet.

Senge argues that any system can be described with these three elements. They are the nouns and verbs of the language; system archetypes are its common sentences.

Escalation: two “defensive” lines make a loop#

Senge’s example is an arms race. Each side saw its build-up as a linear, defensive response to the other’s threat. Put the two lines together and they form a reinforcing loop: one side’s build-up raises the threat the other perceives, which triggers its own build-up, and so on. Each side acted rationally locally, and together they produced the opposite of what both wanted. Senge names this pattern escalation and finds the same structure in gang rivalries, bitter divorces and advertising wars.