Glossary

Each term the book teaches, the chapter teaching it, and its names in other books.

archetype: A named loop structure that recurs across situations, such as fixes that fail, declared on a diagram as a hypothesis by one line of words: Archetype: fixes that fail.; Taught in chapter 10, Archetypes; Other names: pattern, motif
auxiliary: A variable in a stock & flow diagram that neither accumulates nor flows, such as a setting, a capacity or a ratio, drawn as its name alone.; Taught in chapter 6, Auxiliaries; Other names: converter, constant, parameter, aux
balancing loop: A loop that makes a change settle, moving a variable toward a target, with an odd number of − effects, labeled B1, B2 and so on.; Taught in chapter 4, Loops; Other names: negative loop, goal-seeking loop, correcting loop, limit loop
behavior note: A few words on a diagram naming the behavior expected from its structure, such as oscillation or overshoot.; Taught in chapter 4, Behavior notes; Other names: annotation, caption, comment
behavior-over-time graph: A small graph of one quantity over time, drawn beside a diagram as two axes at a right angle, the quantity's name up the vertical and time along the horizontal, with one line of a named shape such as exponential or overshoot and collapse.; Taught in chapter 6, Behavior-over-time graphs; Other names: behavior sketch, behavior trace, behavior curve, goal line
boundary: A thin, solid, rounded outline drawn around a system, with a tab carrying the system's name, separating what the diagram accounts for from what sits outside it.; Taught in chapter 2, The boundary; Other names: system boundary, scope, frame, context
causal loop diagram: A diagram of variables joined by effects, each with its polarity, whose closed paths are declared as reinforcing or balancing loops.; Taught in chapter 4
central outcome: The one variable an influence map is drawn around, its name double-underlined.; Taught in chapter 3, The central outcome; Other names: center, root, goal
cloud: Where a flow's material comes from or goes to outside the model, drawn as a small scalloped outline with no name, at the end of exactly one flow.; Taught in chapter 6, Clouds; Other names: external pool
cluster: Two or more variables of an influence map that share something, drawn within four corner brackets, a label inside the top-left one naming what they share.; Taught in chapter 3, Clusters; Other names: group, theme, category
controlled variable: The quantity the corrective action holds near the target, such as room temperature, with controlled variable written in small type above its name, or above its stock's box where it accumulates.; Taught in chapter 8, Controlled variable; Other names: process, plant, process variable, controlled process
corrective action: The variable changed to close the gap, such as boiler output, with corrective action written in small type above its name.; Taught in chapter 8, Corrective action; Other names: actuator, control action, manipulated variable
deadband: A range of gaps within which the corrective action stays as it is, written beside the middle of the signal from the gap to the corrective action: deadband ±3 cents.; Taught in chapter 9, Deadband; Other names: tolerance, hysteresis
delay: Two short strokes across an effect or a flow, meaning that the change, or the material, arrives well after its cause.; Taught in chapter 4, Delays; Other names: lag, latency, delay mark
effect: A line with an arrowhead from one variable to another, meaning that a change in the first changes the second.; Taught in chapter 1, Effects; Other names: link, arrow, edge, connector, arc, relationship
evidence coding: Solid and dashed lines on effects, the author's judgment of how well supported each effect is as a causal mechanism: in a diagram with a dashed effect, a solid effect is more supported and a dashed one less supported, a hypothesis; where the author draws the line between them is a decision a reader can question.; Taught in chapter 1, Evidence coding; Other names: confidence, certainty, strength
exchange: One named thing crossing the boundary between the system and an external entity, drawn as a solid line with one arrowhead joining the entity's oval to the boundary, its name beside its middle.; Taught in chapter 2, Exchanges; Other names: flow, interface, channel, message
external driver: A variable outside every boundary that affects something inside and is not affected back, its name drawn in angle brackets: ‹regional population›.; Taught in chapter 5, External drivers; Other names: exogenous variable, input, driver, disturbance, load, perturbation
external entity: A party outside the boundary that the system exchanges something with, such as a person or an organization, drawn as its name in an oval.; Taught in chapter 2, External entities; Other names: actor, stakeholder, user, external system
feedback control diagram: A diagram of corrective action holding a quantity near a target, drawn as a causal loop diagram is, with the part each variable plays in its control loop, such as target or measured value, written in small type above its name.; Taught in chapter 8
feedforward: A path of signals from an external driver to a corrective action that passes through no gap, so the correction starts before any gap opens, with no mark of its own.; Taught in chapter 9, Feedforward; Other names: anticipation, predictive action
flow: Material moving into or out of a stock, drawn as a double line with an arrowhead where the material goes and, at its middle, a valve with the flow's name beside it.; Taught in chapter 6, Flows; Other names: pipe, rate valve
fundamental solution: A variable standing for a remedy that acts on the cause, more slowly than a symptomatic solution, with fundamental solution written in small type above its name.; Taught in chapter 10, Symptomatic and fundamental solutions; Other names: root-cause fix, real solution
gap: The difference between the value someone wants and the value they have, drawn as a variable of its own, which a balancing loop closes.; Taught in chapter 4, The gap; Other names: error, discrepancy, deficit, shortfall, comparator
influence claim: An effect in an influence map with no + or −, drawn as a solid line with an arrowhead: one variable bears on another, in a direction not yet known.; Taught in chapter 3, Influence claims; Other names: soft link, association, correlation
influence map: A diagram of what bears on one central outcome, each influence claim with a weight where ranked and a polarity where its direction is measured, the variables gathered into clusters.; Taught in chapter 3
leverage point: A variable proposed as the place to intervene, drawn as a box with a question mark at the middle of each side: a hypothesis, not a proven fix.; Taught in chapter 4, Leverage points; Other names: intervention, lever, hatch, solution
loop: A closed path of effects, along which a variable ends up affecting itself.; Taught in chapter 4, Loops; Other names: cycle, circuit, feedback loop
material path: A flow's double line, two thin parallel lines along which material moves, and which never carries a reading.; Taught in chapter 6, Flows; Other names: physical flow, pipe, conveyor
measured value: The controlled variable as it is read, such as thermometer reading, drawn as a variable of its own because a reading can arrive late or stray, with measured value written in small type above its name.; Taught in chapter 8, Measured value; Other names: sensor, sensor reading, measurement, feedback signal
nonlinear effect: An effect that is weak over part of its range and sudden over another, or strong and then flat, drawn with a small S beside its middle.; Taught in chapter 5, Nonlinear effects; Other names: curve, threshold link, nonlinear curve, nonlinear link
override: A variable a person sets whose signal reaches a corrective action, replacing the loop's rule for a while, with override written in small type above its name.; Taught in chapter 9, Override and false alarms; Other names: manual mode, bypass
polarity: The + or − on an effect: + when the two variables move in the same direction, − when they move in opposite directions.; Taught in chapter 3, Causal claims; Other names: sign, valence, positive link, negative link, inhibition link
reinforcing loop: A loop that makes a change grow in whichever direction it starts, with an even number of − effects, labeled R1, R2 and so on.; Taught in chapter 4, Loops; Other names: positive loop, virtuous cycle, vicious cycle, growth loop
saturation: The most a corrective action can reach, however wide the gap, written beneath its name as at most and the limit: at most 2 kW.; Taught in chapter 9, Saturation; Other names: ceiling, clipping
side effect: A consequence of a symptomatic solution, usually delayed, with side effect written in small type above its variable's name.; Taught in chapter 10, Side effects; Other names: unintended consequence, blowback
signal: An effect in a stock & flow or feedback control diagram, a single thin line with an arrowhead carrying a reading of a quantity rather than the quantity itself, and never ending at a stock.; Taught in chapter 6, Signals; Other names: information link, connector, feedback link, info arrow, signal arrow, controller
stock: A quantity that accumulates and changes only through its flows, drawn as a plain box around its name, its units beneath in smaller type.; Taught in chapter 6, Stocks; Other names: level, reservoir, accumulator, pool
stock & flow diagram: A diagram of what accumulates, drawn as stocks, and how it changes, drawn as flows, with auxiliaries and signals setting the flows' rates.; Taught in chapter 6
stock equation: The line beneath a stock's box adding its inflows and subtracting its outflows, as in change in water in tub = filling − draining, or = 0 for a stock with no flows.; Taught in chapter 6, The stock equation; Other names: equation tag, balance equation
symptomatic solution: A variable standing for a remedy that relieves a symptom quickly, with symptomatic solution written in small type above its name.; Taught in chapter 10, Symptomatic and fundamental solutions; Other names: quick fix, band-aid
system archetype: A causal loop diagram carrying a line for each declared archetype and, above some variables' names, a role such as symptomatic solution or side effect.; Taught in chapter 10
system context map: A diagram of one system's boundary, the external entities outside it, and the exchanges crossing between them.; Taught in chapter 2
target: The value someone chooses for a quantity to stay near, such as desired temperature, with target written in small type above its name, and no signal ending at it.; Taught in chapter 8, Target and gap; Other names: setpoint, goal, reference, desired value
variable: A quantity that can rise or fall, named as a noun phrase such as hours slept and never as an action.; Taught in chapter 1, Variables; Other names: factor, element, node, item
viewpoint tag: A small labeled box beside an effect naming who stresses that effect, which marks emphasis and not a different structure.; Taught in chapter 5, Viewpoint tags; Other names: perspective, lens, color coding
weight: Where influences are ranked, an influence's relative importance, drawn as one, two or three dots beside the middle of its line.; Taught in chapter 3, Weight; Other names: strength, thickness, priority