The term affordance was coined in 1977 by psychologist James J. Gibson, one of the founders of perceptual psychology. Gibson defined the concept as the actions that are possible within an environment and within the context of an actor’s capacity. The concept is illustrated through the stairs metaphor: the height of the step in relationship to the actor's size affords stepping up. These possibilities for action exist whether the actor realizes it or not. Gibson's definition is still used in perceptual and cognitive psychology when studying an actor’s behavior in his environment, as well as in computer, web, and industrial design.
The fields of human computer interaction (HCI) and interaction design have made great use of the concept of affordances. Donald Norman, a leader in design and usability, derived the term "perceived affordances" from Gibson’s work. In the case of perceived affordances, the affordances of interest are those the actor realizes exist when interacting with an item.
In the HCI and interaction design fields, it is important to consider the usability of interacting with a machine, such as a computer. Towards this end, a designer will choose elements designed to convey the actions, or affordances, that will be enabled when the user selects them. In web design, the reverse, start, stop, and forward button graphics that are used in many Internet video players are examples of affordances.
Physical constraints and cultural conventions also help determine the usability of an item. In some situations, designers may refer to these considerations as affordances. In the HCI discipline, a computer's screen width provides an example of physical constraint, and designers often try to keep a screen design within the limits of the users’ screen sizes. An example of the influence of culture is using an envelope icon to allow a user to send an email. The envelope would mean nothing to someone who had no experience with receiving paper mail through a postal system.
Along with HCI and interaction design, the discipline of industrial design also relies on an understanding of perceived affordances. The effective use of these can be critical to a product’s success. When product designers think through a user’s behavior and relationship to a product, he may make design choices that can improve the product’s usability, market acceptance, and safety.
The use of perceived affordances in commercial design can help people move through their environment more easily. In commercial buildings, the design of door handles affects whether people attempt to pull or push a door open. Matching the handle design to the movement of the door can ease traffic flow.