Affordances and Signifiers

Definition

An affordance is a relationship between an object and an agent — what actions are actually possible (a flat plate affords pushing, a knob affords turning). A signifier is whatever perceivable signal tells the agent where and how to act — a label, a shape, a sound, even an accidental cue like a worn path. Norman's key correction: "Affordances determine what actions are possible. Signifiers communicate where the action should take place." Good design needs both, but signifiers are what designers can actually control.

In the Book

Norman opens Chapter 1 by tracing "affordance" to psychologist J. J. Gibson, then narrows it for design use, since designers had started misusing the term to mean "a thing I placed on the screen." He separates the two ideas cleanly with the problem-door example (Figure 1.2): identical push-bar hardware on two doors, one meant to be pulled and one pushed — the affordance (pushing) is visible, but without a sign (a signifier), users guess wrong roughly half the time. He also gives the London hotel sink whose drain stopper had no visible signifier at all, forcing a trip to the front desk, and the rubber traffic pipes in a public park that presented an "anti-affordance" (blocking cars) while secretly permitting authorized vehicles through — a deliberately misleading signifier. Chapter 4 extends the pair to sound (auditory signifiers, like a camera's fake shutter click) and to touchscreens, where the affordance of touching exists everywhere on the glass but signifiers must indicate exactly where.

Why It Matters

This distinction separates two different design failures that get conflated: making an action physically possible versus making it discoverable. A system can have the right affordance (the button really does work) and still fail because nothing signifies its existence or purpose — the fix for "nobody uses this feature" is often a signifier problem, not a capability problem. The pair generalizes past physical objects to interfaces, organizations, and signage of any kind: wherever someone has to guess what they're allowed to do and how, the diagnosis is either "the possibility isn't really there" or "the possibility isn't signaled," and the remedies are different.