What is a mental model?

Why it matters

When users open your product, they don’t start from zero. They build their mental model from products they have used before. Nielsen Norman Group connects this with Jakob’s law: people spend most of their time on other websites and expect yours to work the same way.

The designer, by contrast, knows the product down to the smallest detail, and so assumes everything is clear. NN/g counts this gap among the biggest dilemmas of usability. When the two models don’t fit, usability suffers first.

Don Norman’s three models

In his book The Design of Everyday Things, Don Norman distinguishes three models. The book first appeared in 1988 under the title The Psychology of Everyday Things.

The design model is how the designer intends the product to work. The user’s model is the mental model that forms in the head during use. In between is the system image: interface, labels, instructions, documentation.

Norman’s key observation: the designer can’t talk to the user directly. All communication runs through the system image. If the system image doesn’t show the design model clearly, the user builds the wrong model.

Example: the difference between “Archive” and “Delete”

The Archive and Delete buttons in email apps show this well. Both take the email out of the inbox, so they are easy to mix up. Guess first, then open the answer.

Anyone who thinks they deleted an archived email sees it back in the inbox as soon as someone replies. And the other way round: anyone who thinks they archived an important email but deleted it loses it after 30 days.

The same problem can come up in banking apps. Users may take the balance shown for the money they can spend. But if there is a pending transaction, the two numbers can differ. If the label doesn’t state this difference, users decide with the wrong model.

How to close the gap

NN/g names two ways. The first is to adapt the system to users’ model. NN/g recommends this when most users’ models resemble each other. You find this shared model in information architecture work with card sorting.

The second is to correct the user’s model: clearer labels, explanations, a guide on first use.

A good way to see the user’s model is a think-aloud test. While carrying out a step, the user says what they expect. You compare the expectation with the result.

If you are doing a UX audit, I recommend asking one question of every button label: does this name correctly predict what happens on click?

Often confused: the conceptual model

The mental model is in the user’s head, and nobody can draw it directly. The conceptual model, by contrast, is the explanation the designer deliberately offers. For Norman, giving users a good conceptual model is one of the principles of good design.

So the conceptual model is the side you control. The mental model is the result of how well it was conveyed. User-centred design rests on this idea too.