James Gibson and Affordances

Affordances are measured relative to the observer (will that board hold me up? Can I fit through that opening? Can I sit on this?). We see things in the world according to our purposes, and our purposes are not always reflective or conceptual purposes. Our bodies know what they need to sit on, what they need to fit into, what they need to fear, and so forth, and we use concepts when there is some question or need for reflective ability. It means that we do not simply see the existence and properties of a thing, but also the meaning or value of a thing. This is not after the fact, but part of the perception itself.

"The affordances of the environment are what it offers the animal, what it provides or furnishes, either for good or ill. The verb to afford is found in the dictionary, but the noun affordance is not. I have made it up. I mean by it something that refers to both the environment and the animal in a way that no existing term does. It implies the complementarity of the animal and the environment...

"If a terrestrial surface is nearly horizontal (instead of slanted), nearly flat (instead of convex or concave), and sufficiently extended (relative to the size of the animal) and if its substance is rigid (relative to the weight of the animal), then the surface affords support...

"Note that the four properties listed --- horizontal, flat, extended, and rigid --- would be physical properties of a surface if they were measured with the scales and standard units used in physics. As an affordance of support for a species of animal, however, they have to be measured relative to the animal. They are unique for that animal. They are not just abstract physical properties."

Gibson, James. J. The Ecological Approach to Visual Perception. 1979. (p. 127)

There are three fundamental properties of an affordance:

  1. An affordance exists relative to the action capabilities of a particular actor.
  2. The existence of an affordance is independent of the actorís ability to perceive it.
  3. An affordance does not change as the needs and goals of the actor change.

To elucidate the first property Gibson gives the example of a horizontal, flat, extended, and rigid surface that affords support. A given surface that provides support for one actor, may not provide support for another actor (perhaps because of a differential in weight or size). There is only one surface in question here, yet the affordance of support exists for one actor whereas it does not exist for another. Note that the affordance is not a property of the experience of the actor but rather of the action capabilities of the actor. Also note that even if the surface is not intended to provide support, if it does in fact support a given actor, then the affordance of support exists. The second and third properties point to the fact that an affordance is invariant.

Defined in this way, affordances cut across the subjective/objective barrier. They are objective in that their existence does not depend on value, meaning, or interpretation. Yet they are subjective in that an actor is needed as a frame of reference. By cutting across the subjective/objective barrier, Gibsonís affordances introduce the idea of the actor-environment mutuality; the actor and the environment make an inseparable pair.

Joanna McGrenere & Wayne Ho, "Affordances: Clarifying and Evolving a Concept" http://www.dgp.toronto.edu/~joanna/papers/gi_2000_affordances.pdf