The Design of Everyday Things

Signifiers can be deliberate and intentional, such as the sign PUSH on a door, but they may also be accidental and unintentional, such as our use of the visible trail made by previous people walking through a field or over a snow-covered terrain to determine the best path.

Many people find affordances difficult to understand because they are relationships, not properties.

Discoverability results from appropriate application of five fundamental psychological concepts covered in the next few chapters: affordances, signifiers, constraints, mappings, and feedback.

It is the duty of machines and those who design them to understand people. It is not our duty to understand the arbitrary, meaningless dictates of machines.

Feedback—communicating the results of an action—is a well-known concept from the science of control and information theory.

To summarize: • Affordances are the possible interactions between people and the environment. Some affordances are perceivable, others are not. • Perceived affordances often act as signifiers, but they can be ambiguous. • Signifiers signal things, in particular what actions are possible and how they should be done. Signifiers must be perceivable, e

But as soon as there is a problem or a misunderstanding, the problems arise.

There we have it. Seven stages of action: one for goals, three for execution, and three for evaluation (Figure 2.2). 1. Goal (form the goal) 2. Plan (the action) 3. Specify (an action sequence) 4. Perform (the action sequence) 5. Perceive (the state of the world) 6. Interpret (the perception) 7. Compare (the outcome with the goal) The seven-stage a

An affordance is a relationship between the properties of an object and the capabilities of the agent that determine just how the object could possibly be used.