An affordance is a relationship between the properties of an object and the capabilities of the user that determine just how the object could possibly be used.
Perceived affordances help people figure out what actions are possible without the need for labels or instructions.
Affordances determine what actions are possible. Signifiers communicate where the action
should take place.
Design requires both.
Electronic book readers do not have the physical structure of paper books, so unless the software designer deliberately provides a clue, they do not convey any signal about the amount of text remaining.
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, else they fail to function.