Affordances

Definition: An affordance is a relationship between the properties of an object and the capabilities of the agent (person, animal, machine) that determine how the object could possibly be used. A chair affords support → sitting; most chairs afford lifting (but not for a weak person — so for them the affordance does not exist).

Key claims:

• An affordance is not a property of an object — it is a relationship. This is why people find it hard.
• Affordances exist whether or not they are perceivable. A perceived affordance is one the agent can detect.
• Anti-affordance = prevention of interaction (e.g., glass blocks passage). Anti-affordances must also be discoverable, or harm follows (birds/people hit glass).
• Origin: J.J. Gibson (ecological psychology, "direct perception," "information pickup"). Norman adapted the term for design.

Affordance vs perceived affordance vs signifier

• Affordances = the possibilities (some perceivable, some not).
• Perceived affordances often act as signifiers, but can be ambiguous.
• If an affordance/anti-affordance can't be perceived, you need a separate signal → a signifier.

Design takeaway

For physical objects, visible affordances give strong clues (a flat plate affords pushing; a knob affords turning). But because affordances are confusing for virtual objects (a touchscreen affords touching everywhere), Norman argues designers should mostly focus on Signifiers, not affordances. See The Six Fundamental Principles of Interaction.

Confidence

1.0 — central, explicitly defined concept; relational definition stated repeatedly.

Sources: ["DOET ch.1 'Affordances' p.10-13"]