brightly colored food

Don Norman lays down the law about what each really means. A couple of years old, but this stuff never goes out of style.

In POET [Psychology of Everyday Things], I argued that understanding how to operate a novel device had three major dimensions: conceptual models, constraints, and affordances. These three concepts have had a mixed reception.

To me, the most important part of a successful design is the underlying conceptual model. This is the hard part of design: formulating an appropriate conceptual model and then assuring that everything else be consistent with it. I see lots of token acceptance of this idea, but far to little serious work. The power of constraints has largely been ignored. To my great surprise, the concept of affordance was adopted by the design community, especially graphical and industrial design. Alas, yes, the concept has caught on, but not always with complete understanding. My fault: I was really talking about perceived affordances, which are not at all the same as real ones.