Overview

A chair offers somewhere to sit, while a handle gives someone something to grasp. Both illustrate affordances: possibilities for action that depend on the relationship between something and the person interacting with it.

The concept comes from ecological psychology. James J. Gibson used the term to describe what an environment makes possible for an animal, including humans. An affordance depends on the object and the person using it - a step that someone can comfortably climb may be too high for a small child or completely inaccessible to someone using a wheelchair. [1]

Affordances became influential in design because they can be a useful way to think about the relationship between people and the things we make. A product can support an action without making that possibility obvious. Conversely, something can appear interactive without actually doing anything.

That distinction matters particularly in digital interfaces, where the possibilities for interaction can be less obvious than they are with physical objects.

In practice

Designer and cognitive scientist Don Norman brought affordances into mainstream design discussion through The Psychology of Everyday Things, later published as The Design of Everyday Things. He subsequently argued that designers needed to distinguish between the actions something actually allows and the actions people believe it allows. [2]

Take a button in a digital interface as an example. The software may allow someone to submit a form by selecting a particular area of the screen, but how does the person know that area is even interactive?

A border, label, familiar shape or visual treatment can communicate what to do. Norman calls these cues signifiers. They indicate where an action can take place or how it should be performed. [3]

This is an important distinction because the word affordance is sometimes used to describe any visual feature that suggests interactivity. The shadow on a button, for example, is often called an affordance. More precisely, it may function as a signifier: a visual cue that helps someone recognise the possibility of clicking or tapping.

The distinction also applies beyond individual controls. A search field may technically accept text, but people still need to recognise its purpose, understand what they can search for and know how to submit a query.

Considerations

Perception and discoverability

An affordance doesn't have to be obvious to exist, nor does it have to be desirable.

William Gaver explored these ideas in his 1991 paper Technology Affordances, describing how possibilities for action can be perceptible, hidden or misleadingly suggested. If people don't recognise an available action, they may never use it. Misleading cues can also suggest actions that aren't possible. [4]

Different people, different possibilities

Designers also need to question whose capabilities they're assuming.

A gesture-based interaction might be available to someone with precise motor control but difficult or impossible for someone else. An interface that relies entirely on visual cues may conceal important actions from people using screen readers. Familiarity matters too: what seems obvious to an experienced user may be unfamiliar to someone encountering the same interaction for the first time.

These differences are a reason to investigate how people actually interact with a design, rather than assuming that an intended action will be apparent or available to everyone.

Interpretations and limitations

There's also a conceptual limitation worth acknowledging. Researchers have continued to debate how affordances should be defined and perceived, and the term has developed different meanings across ecological psychology, human-computer interaction, and design. [5]

For everyday design work, the most useful questions are often straightforward: What can someone do here? What might they think they can do? And what, if anything, prevents them from doing it?