Mental model
An internal working scale-model of how some piece of the world behaves.
What it means
A mental model is a person's internal representation of how a system, situation, or device works, used to reason, explain, predict, and act without manipulating the real thing. In reasoning research, Johnson-Laird's mental model theory holds that people reason not by applying formal logic but by constructing concrete models of the possibilities a statement allows and inspecting them, which predicts characteristic errors when relevant possibilities go unrepresented. Mental models are typically incomplete, unstable, and 'runnable' only approximately, yet they make complex inference tractable. They underwrite expertise, troubleshooting, and the usability of interfaces, since a designer's model and a user's model often diverge. Improving a faulty mental model, rather than memorizing outputs, is what produces transferable understanding.
Examples
Someone who pictures a thermostat as a 'valve' turns the heat to maximum to warm a room faster, because their mental model says higher setting means faster flow.
People jab the lift button repeatedly because their model says each press adds urgency; the lift's actual logic registered the call once and ignores every extra push.
Someone convinced that closing background apps saves battery swipes them all away nightly, though the phone had already suspended them — a tidy model of a system that does not work that way.
First described in Kenneth Craik (1943); Philip Johnson-Laird (1983).