Hans J Eysenck is somewhat difficult to identify or classify. He supports a model of personality characterized by types and traits because he firmly beliefs that the most fundamental personality characteristics are inherited. His equally strong belief that both heredity and environment determine behavior supports his active verbal support of learning theory and the behavior therapies.
Eysenck does not keep his nose to only one grindstone, and refuses to be neatly categorized as a theorist. He has involved himself with such topics as the relation between smoking and health, criminality, the heritability of intelligence, educational theory and practice, sexual behavior, the effects of psychotherapy, and even astrology; in addition to personality theory and behavior therapy. These wide-ranging interests are a partial cause of his ability that equals and compete with Cattell's: Eysenck's most recent bibliography (1982) lists around 40 books and over 600 articles and chapters.