Mental models

A set of parts connected so that a change in one can spread to others through the links.

52 disciplines

A loop where an effect feeds back to change its own cause. Reinforcing loops amplify change; balancing loops resist it.

49 disciplines

When getting more of one thing means accepting less of another, because resources or constraints are limited.

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A stock is an amount that accumulates; flows are the rates that add to or drain it. The stock changes only when inflow and outflow differ.

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Anything that reduces uncertainty. It can be encoded into a signal, sent across a channel, and decoded — and noise can corrupt it on the way.

38 disciplines

Energy is never created or destroyed; it changes from one form into another, and some is always lost as heat.

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Limits that decide what is possible. Usually one binding constraint — the bottleneck — governs the outcome until it is relieved.

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One thing genuinely bringing about another — as opposed to two things merely moving together. Establishing it needs a mechanism and controls, not just a pattern.

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How a system's size changes what matters about it. Quantities rarely scale in step: doubling a length can quadruple an area and multiply a volume eightfold.

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A way to reason about uncertainty by assigning each possible outcome a share of the whole, between impossible (0) and certain (1).

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When many simple parts interacting by simple rules produce a pattern or behaviour that none of the parts has on its own.

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A repeated back-and-forth movement around a central value. How often it repeats is its frequency; how far it swings is its amplitude.

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A level below which little happens and above which the behaviour changes sharply — sometimes irreversibly.

25 disciplines

When each step's growth is added to the base so the next step grows too — producing accelerating, exponential change rather than a steady line.

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A disturbance that travels and carries energy from place to place without carrying the material itself along with it.

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Real data mixes a meaningful pattern (signal) with random variation (noise); the skill is telling them apart before you act on either.

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Searching a space of options for the best one under constraints — following a gradient of 'better' toward a maximum or minimum.

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A state where opposing processes balance so the whole stops changing overall — even though activity continues underneath.

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Systems nest inside systems — parts form wholes that are themselves parts of larger wholes, each level with its own rules and language.

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Countless small random steps carry things from where they are crowded to where they are sparse — smoothing differences and spreading through a network.

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When many varying candidates are filtered by a criterion and the survivors are copied, the population adapts to the criterion over rounds — with no designer.

14 disciplines

Some quantity stays constant no matter how a system rearranges — it can move or transform but is never created or destroyed.

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Left alone, systems drift toward their most probable, most spread-out states — giving processes a direction in time that is hard to reverse.

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Harm reaches a target only when a source, a connecting pathway and an exposed receptor all exist; break any link and the harm does not arrive.

12 disciplines

Something stays the same under a change — rotate, reflect, shift or relabel it and a key property is unchanged. What is preserved is often the deep truth.

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Build a complex whole from separable, reusable parts with clean interfaces, so each can be understood, changed or replaced on its own.

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A thing defined in terms of smaller copies of itself — solve the small case and the same rule builds the whole, often looking similar at every scale.

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A belief's strength should be revised by combining how likely it was beforehand (the prior) with how strongly new evidence bears on it.

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Reliability comes not from one perfect barrier but from stacking several independent, imperfect barriers, so a threat must breach all of them at once.

5 disciplines

Confidence in a conclusion grows when several independent lines of evidence, each with different weaknesses, point the same way.

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Agents respond to costs and rewards; to understand or change a system's behaviour, look at what each part is rewarded for — not what it's told to do.

3 disciplines