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UX glossary

Mental Model

A mental model is the idea people form of how something works. It’s based on experience and assumptions, not on how the system actually works under the hood.

Imagine someone wants to free up space on their laptop and deletes a few old holiday photos from a synced cloud folder. The assumption behind it: “Gone from the laptop, still safe in the cloud.” A few days later, the photos have vanished from their phone too. Technically, everything worked as designed. The picture in their head just didn’t match what the system actually does.

Explained simply

A mental model is the idea a person forms of how something works. The Nielsen Norman Group describes it, in essence, as what someone believes about a system. The key word is “believes”: mental models aren’t based on facts but on experience, assumptions and habits. They help us predict what will happen when we press a button.

Here’s an everyday comparison: many people turn the thermostat all the way up so the room warms up faster. Behind that is the idea that the dial works like a faucet: open it further, get more heat. In reality, a thermostat regulates toward a target temperature. The room usually doesn’t heat up any faster, it just ends up too warm. Researcher Willett Kempton studied this kind of folk theory in 1986.

The term goes back to Scottish psychologist Kenneth Craik, who argued in “The Nature of Explanation” (1943) that the mind builds small-scale models of reality to anticipate events. The idea was brought into design mainly by Don Norman in his book The Design of Everyday Things, first published in 1988 as “The Psychology of Everyday Things”.

How models drift apart

Norman distinguishes three levels: the model in the design team’s heads, the so-called system image (everything the product visibly shows and how it responds) and the user’s model. Design teams can only “talk” to users through the system image. If it’s misleading, users end up with a different model from the one intended.

On top of that, people bring expectations from other products. Jakob Nielsen put this into words as “Jakob’s Law”: users spend most of their time on other websites, so they expect yours to work the same way. You’ll find more principles like this in the Laws of UX collection.

An example

Back to the cloud folder. Before, the app only shows a brief “File deleted” message. After the redesign, a notice appears: “This file will be deleted on all your devices. You can restore it from the trash for 30 days.” The system works exactly as before. But the system image now explains what really happens, and users’ mental models adjust.

In practice

  • Observe instead of asking. Have people think aloud during a usability test. When they say what they expect to happen next, you’re hearing their mental model directly.
  • Adapt the product first. Where possible, the system should match people’s expectations, for example in how the navigation is structured. Card sorting shows you how people mentally group content.
  • Explain where you have to deviate. When a system works differently than people expect, clear labels and short hints at the right moment help more than a long tutorial.

Related terms

Affordance, Information Architecture, Card Sorting

Sources

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