Cosnier discusses the evolution of Freud's thought concerning memory, and how this ultimately led him to the metaphor of the mystic writing pad. An intimate relationship existed between Freud's practice and the creation of models, including metaphors at different levels of abstraction, to describe the relations between the past and the present. Cosnier develops the concept of instruments of knowledge, important for the development of Freud's theoretical thinking. The notion of transference, which Freud was able to discern in his observations of Breuer's experience with Anna O., functioned as an instrument of knowledge. This instrument was able to take Freud much farther in generalization than hypnosis and the notion of the hypnoid state, since it immediately differentiated past and present. The author