Our concepts and theories in psychoanalysis have an unpredictable and unmeasurable “half-life” with respect to their continued heuristic potential and the ingenuity with which they may account for and order most of the significant clinical observations at any particular historical period in our field. It is remarkable, therefore, how felicitous and enduring many of our key concepts appear to have been, in that they have, on the whole, retained their usefulness for a long period, and up to a point, have not unduly hampered clinical and theoretical progress. This has undoubtedly been due to the fact that the formulation of many of our basic concepts has left enough room for the accrual of new and varied meanings, based on the accumulation of additional clinical observations and interpretations. Not only did these concepts and theories initially adequately encompass the most relevant clinical facts from which they arose, but they have also raised these very facts to a level of