Abstract

The aim of this thesis is to investigate the relationship between models of human nature and psychology. A central claim is that all psychological theories necessarily presuppose a model of human nature and by virtue of this, a broad metaphysical theory. Following a brief review of some of the multi-disciplinary literature concerned with models of human nature it is concluded that certain implications follow from adopting a particular model. For example implications for social science research and the interpretation of behaviour. A survey of the psychological literature reveals that two models have tended to dominate the debate, an agency model and a deterministic model. The relevance and importance of philosophical debate in psychology is established. A conceptual framework is developed that permits the construal of metaphysical systems as theories in the same sense that scientific theories are. The question of how to evaluate theories is discussed and a criterion outlined. It is argued that different metaphysical theories underlie the psychological theories associated with humanistic, behavioural and system theories. These metaphysical theories generate different notions of causality, epistemology and explanation in psychology. Each is critically evaluated and the metaphysical theory underlying systems therapy is found to be the most powerful. The thesis concludes with a discussion of some of the implications for clinical psychology. It is claimed that a systems ontology enables psychologists to avoid the pitfalls of eclecticism and promotes a unified and pluralistic conception of clinical practice.