This is David Pye's classic book on the theory of design. In it, he explores the many facets of good design, including the relationship of aesthetics with function.
A treatise on the essential nature of design as a human activity, its relation to art, science, technics, form, function, aesthetics, and worksmanship. This is one of those books that is not very directly practical--in other words not a very modern book. I love books like that. Pye was a professor of furniture design at the British Royal College of Art. His discussion is wide-ranging and useful only in that deep sense of utility that comes from a thorough understanding rather than in the modern sense of "how to." What I mean to say is that it is the best kind of useful.