The official view of theory testing in the philosophy of science, the deductive model, does not reflect the way ambiguous, vague and ill formulated theories are tested. A new model of theory testing, the explicative model, is outlined which reflects how such theories are tested. This model is illustrated in the actual testing of psychoanalysis, a typical case of an ambiguous, vague and ill formulated theory and is contrasted with Kuhn's notion of the articulation of a paradigm.