"Reflective Practice" is about "knowledge-in-action," an intuitive, often undescribable approach that is more craft than process. Schon looks at the practice of medicine, law, engineering, architecture and urban planning, and examines the divergence between academia and practice (also described as the dilemma between academic rigor and practical relevance). He argues that skilled practitioners exhibit "a kind of rigor that is both like and unlike the rigor of scholarly research..."
Schon writes about the practitioner who makes "innumerable judgments of quality for which he cannot state adequate criteria, and he displays skills for which he cannot state the rules and procedures." It's basically the antithesis of the idea that "if you can't describe what you do as a process, you don't know what you're doing."
Schon says a good practitioner does indeed "know" what he or she is doing. The knowledge is expressed in the action, because words and diagrams are inadequate to convey the knowledge. He's quite critical of the positivist model of technical rationality and its belief that "empirical science was not just a form of knowledge but the only source of positive knowledge of the world." In contrast, Schon asserts that "competent practitioners usually know more than they can say."
It's a great book - albeit heavily intellectual and occasionally a bit dry. But I love it and heartily recommend picking up a copy.