A core mechanism of the psychoanalytic process is described. This involves the effects of treatment on an ongoing "unconscious intrapsychic process," which has specific points of vulnerability to pathology. The concept of an intrapsychic process described by the author in previous publications is an expanded formulation of the idea of thought as trial action and of the signal theory of anxiety. The psychoanalytic method alters the functioning of the ego astride this unconscious process, strengthening its control over anxiety, defense, trauma, and symptom formation. This is mutative in the psychoanalytic method.