Following suggestions in the literature concerning the need for systematic treatment of psychoanalytic theory, we have attempted to introduce new means for generating and classifying the defence mechanisms. The classification results from a consideration of the elementary transformations that may be applied to unconscious propositions of the form actor–action–object. Elementary transformations on the actor, the action or the object of the unconscious proposition are introduced, and the defence mechanisms are then systematically generated by applying one or more of the transformations to unconscious propositions. The relation of the mechanisms thus generated to more classic work is examined, as are several different recent proposals for the study of the defence mechanisms.