This chapter begins with a brief account of the assumptions about understanding and conceptual thinking underlying the discussion. An examination of any philosophical argument will presuppose, either explicitly or implicitly, some general view of the nature of human understanding and conceptual thinking and some corresponding view of the nature of philosophical disagreement. The same pathological behaviour is understood and described with equal consistency and serviceability, but in two co-extensive and mutually exclusive conceptual systems, as either 'demonic possession' or 'schizophrenia'. Conceptual shifts of the kind described have often been likened to the phenomenon of Gestalt switch where, typically, the same visual datum can be organised or interpreted in significantly different ways, as exemplified by the reversal of figure and ground in a line drawing. Pepper maintains that any adequate conceptual system must also be homogeneous, being derived from a single root model.