What is design, and what is art?
This is a complicated question; or else, it has a complicated answer.
Until recently, I defined art as creations done to express one's own self, and design as creations done to achieve some purpose. This separation was rather vague, as expressing ones self is, in fact, a purpose (and thus, art is design).
But tonight, I think I've finally figured it out:
Design is what you don't think about when creating art.
Design is the set of techniques which may be used in creating art. You can't think about it when creating art (which I still describe as expressions of one's self), as it involves too much thinking. Art is about feeling.