Joshua Porter hit the nail on the head with a recent post titled Five Principles to Design By
Art is about personal expression. It is about the life, the emotions, the thoughts and ideas of the artist. It matters very little what observers do, their activity is not required, only their appreciation. The practice of Art doesnâ€™t require them. It is a necessary activity for the artist, and the artist alone.
Design, on the other hand, is about use. The designer needs someone to use (not only appreciate) what they create. Design doesnâ€™t serve its purpose without people to use it. Design helps solve human problems. The highest accolade we can bestow on a design is not that it is beautiful, as we do in Art, but that it is well-used.
Unlike Art, Design is always contextual. It matters when a design was created because of the context of its use: what problem is it supposed to solve? And for whom? At what point in time? This is why design is so related to technology, because technology changes so quickly, so must our designs. A design that worked ten years ago might not even be worth considering today. History is littered with wonderful designs that are no longer necessary.
The litmus test. When people enjoy Art, they say "I like that". When people enjoy Design, they say "That works well". This is not by accident. Good Design is something that works well.