Abstract
Most psychodynamic theories are based on Freud's models of mental dynamics which were significantly influenced by Newtonian physics. Freud's attempts to use the then current scientific metaphors led to theoretical and clinical dilemmas particularly in deep psychotherapy and especially with borderline patients. The author argues that as Newtonian principles are useful for describing macroscopic reality, so Freud's Newtonian constructs are useful to a certain depth of therapy. Beyond that point, scientific metaphors can be retained but the appropriate metaphors are those of quantum physics. Quantum metaphors are used to explore duality, free will and patient-therapist interaction.