There are almost as many explanations for psychiatric disorders as there are patients with them. Each explanation is intriguing, some of them are systematic, all of them have intellectually powerful champions. Yet their very multitude is a scandal. It provokes the professionally debilitating challenge: Why does every psychiatric explanation satisfy some people and not others? Recently this question has received a simple answer. We cannot satisfactorily explain that which we lack the skill to describe. To develop the fundamental skill a student must see many patients under the direction of an experienced and involved instructor to whom he can show his results, accept correction and advance in his abilities. But we need a means to amplify the clinical experience, a text to supplement the instructor in bringing forth and strengthening the vocabulary needed to describe the phenomenology, presentations and distinctions amongst psychiatric patients. A "programmed text" such as this one is a satisfactory means because it can cover rapidly many themes and variations of a vast clinical experi- ence. It can permit the reader to progress at his own speed but bring a sense of mastery to him as he progresses. He can check his knowledge as he sees patients on the clinical services. This kind of text combined with patient practice is thorough, fast and fun, but should succeed in the important task of rapidly building for the student an authentic set of terms and concepts suitable for both clinical work and research.