Ego Development and Psychopathology presents an original theoretical underpinning for classification and interpretation of the major mental disorders, one based largely on the author's clinical experience. Ausubel's central thesis is that the most significant and crucial factors predisposing persons to mental disorders are critical developmental defects that arise at vital transitional phases of ego development. He sees both normal and pathological personality functioning as most cogently explained in terms of an individual's ego structure at a given point in the life cycle.