An affordance is the possibility of an action on an object or environment.
Additional meanings have developed, largely a result of misinterpretations. The original definition in psychology includes all actions that are physically possible. When the concept was applied to design, it started also referring to only those action possibilities which one is aware of.
The word is used in a variety of fields: perceptual psychology, cognitive psychology, environmental psychology, industrial design, human–computer interaction (HCI), interaction design, communication studies, instructional design, science, technology and society (STS), and artificial intelligence.
As action possibilities
Psychologist James J. Gibson originally introduced the term in his 1977 article "The Theory of Affordances" and explored it more fully in his book The Ecological Approach to Visual Perception in 1979. He defined affordances as all "action possibilities" latent in the environment, independent of an individual's ability to recognize them, but always in relation to agents (people or animals) and therefore dependent on their capabilities. For instance, a set of steps which rises four feet high does not afford the act of climbing if the actor is a crawling infant. Gibson's is the prevalent definition in cognitive psychology.
Affordances were further studied by Eleanor J. Gibson, wife of James Gibson, who created her theory of perceptual learning around this concept. Eleanor Gibson's book, An Ecological Approach to Perceptual Learning and Development explores affordances further.
As perceived action possibilities
In 1988, Donald Norman appropriated the term affordances in the context of human–machine interaction (HCI) to refer to just those action possibilities that are readily perceivable by an actor. Through his book The Design of Everyday Things, this interpretation was popularized within the fields of HCI and interaction design. It makes the concept dependent not only on the physical capabilities of an actor, but also on their goals, beliefs, and past experiences. If an actor steps into a room containing an armchair and a softball, Gibson's original definition of affordances allows that the actor may throw the chair and sit on the ball, because this is objectively possible. Norman's definition of (perceived) affordances captures the likelihood that the actor will sit on the armchair and throw the softball. Effectively, Norman's affordances "suggest" how an object may be interacted with. For example, the size, shape and weight of a softball make it perfect for throwing by humans, and it matches their past experience with similar objects. The focus on perceived affordances is much more pertinent to practical design problems, which may explain its widespread adoption.
Norman later explained that this restriction of the term's meaning had been unintended, and that he would replace it by "perceived affordance" in any future revision of the book. However, the definition from his book has been widely adopted in HCI and interaction design, and both meanings are now commonly used in these fields.
Following Norman's adaptation of the concept, affordance has seen a further shift in meaning where it is used as an uncountable noun, referring to the easy discoverability of an object or system's action possibilities, as in "this button has good affordance". This in turn has given rise to a use of the verb afford – from which Gibson's original term was derived – that is not consistent with its dictionary definition (to provide or make available): designers and those in the field of HCI often use afford as meaning "to suggest" or "to invite".
The different interpretations of affordances, although closely related, can be a source of confusion in writing and conversation if the intended meaning is not made explicit and if the word is not used consistently. Even authoritative textbooks can be inconsistent in their use of the term.
William Gaver divided affordances into three categories: perceptible, hidden, and false.
- A false affordance is an apparent affordance that does not have any real function, meaning that the actor perceives nonexistent possibilities for action. A good example of a false affordance is a placebo button.
- A hidden affordance indicates that there are possibilities for action, but these are not perceived by the actor. For example, it is not apparent from looking at a shoe that it could be used to open a wine bottle.
- For an affordance to be perceptible, there is information available such that the actor perceives and can then act upon the existing affordance.
This means that, when affordances are perceptible, they offer a direct link between perception and action, and, when affordances are hidden or false, they can lead to mistakes and misunderstandings.
- James J. Gibson (1977), The Theory of Affordances. In Perceiving, Acting, and Knowing, edited by Robert Shaw and John Bransford, ISBN 0-470-99014-7.
- James J. Gibson (1979), The Ecological Approach to Visual Perception, ISBN 0-89859-959-8.
- Uexküll, Jakob von (1980 [1920 etc.]), Kompositionslehre der Natur, edited by Thure von Uexküll, Frankfurt am Main.
- Dorion Sagan (2010). "Introduction: Umwelt after Uexküll". In Jakob von Uexküll; Marina von Uexküll; Joseph D. O'Neil. A Foray Into the Worlds of Animals and Humans: With a Theory of Meaning (Joseph D O'Neil translation of 1940 ed.). University of Minnesota Press. p. 5. ISBN 9781452903798.
Organisms in their life-worlds recognize not only sensory inputs, but also functional tones, the use they need to make of certain stimuli if they are to do what they need to survive.
- Donald Norman, The Design of Everyday Things, ISBN 0-465-06710-7. Originally published under the title The Psychology of Everyday Things, often abbreviated to POET.
- Donald A. Norman (1999). Affordance, Conventions and Design. Interactions 6(3):38-43, May 1999, ACM Press.
- Affordance, Conventions and Design (Part 2)
- Human–Computer Interaction, Preece et al. (1994, p. 6): The authors explicitly define perceived affordances as being a subset of all affordances, but another meaning is used later in the same paragraph by talking about "good affordance."
- Universal Principles of Design, Lidwell, Holden & Butler (2003, p. 20): The authors first explain that round wheels are better suited for rolling than square ones and therefore better afford (i.e. allow) rolling, but later state that a door handle "affords" (i.e. suggests) pulling, but not pushing.
- Gaver, William W. (1991). "Technology affordances". Proceedings of the SIGCHI conference on Human factors in computing systems Reaching through technology - CHI '91. p. 79. doi:10.1145/108844.108856. ISBN 0897913833.
- "Placebo buttons, false affordances and habit-forming"
- The role of affordances in evolution and niche construction is discussed by Rob Withagen; Margot van Wermeskerken (2010). "The role of affordances in the evolutionary process considered: A niche construction perspective". Theory and Psychology 20 (4): 489–510. doi:10.1177/0959354310361405.
- The role of affordances in agency is discussed by Rob Withagen; Harjo J de Poel; Duarte Araújo; Gert-Jam Pepping (2012). "Affordances can invite behavior: Reconsidering the relationship between affordances and agency" (PDF). New Ideas in Psychology 30 (2): 250–258. doi:10.1016/j.newideapsych.2011.12.003.
- Affordance and computation is discussed by AJ Wells (2002). "Gibson’s affordances and Turing’s theory of computation" (PDF). Ecological psychology 14 (3): 140–180. doi:10.1207/S15326969ECO1403_3.
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- A series of slides concerning theories of vision and (incidentally) the role of affordances and some interesting optical illusions concerning affordances Aaron Sloman (March 12, 2014). "What's vision for, and how does it work? From Marr (and earlier) to Gibson and beyond" (PDF). Retrieved May 22, 2014.