This report explores the interface between psychiatry and the DSM-III, arguing that philosophy and psychiatry are of value to one another. Three trends within philosophy are delineated--positivism, hermeneutics, and a synthetic position. These trends are applied to the DSM-III and to specific issues in psychiatric nosology such as the definition of mental disorder, the question of establishing boundaries between different psychiatric disorders, and the differentiation of organic and functional disorders. It is argued that while nosologists often think of themselves along positivist lines, and are often criticized by hermeneutic thinkers for just these assumptions, a synthetic view accounts best for how psychiatric science works. It is concluded that philosophy undergirds psychiatric nosology, while psychiatric nosology raises a series of philosophical questions.