CONCEPT formation in the normally functioning person is marked by the capacity to interpret experience at appropriate levels of abstraction. It is generally agreed that schizophrenia is characterized by impaired cognitive focusing (see Chap. 4) and disturbed reasoning (see Chap. 5), but divergent opinions exist as to (a) whether schizophrenic persons suffer any basic deficit in abstracting ability and (b) whether such deficits, even if present, differ in any diagnostically useful way from the conceptual impairments demonstrated by persons with organic brain disease. It is therefore helpful to introduce this chapter with a brief review of the major theoretical positions and experimental data concerning conceptual deficit and abstract thinking in schizophrenia.