Parfit's requirements for an ideal Theory X cannot be fully met since the Mere Addition Principle and Non-Antiegalitarianism imply the Repugnant Conclusion: Theory X does not exist. However, since the Repugnant Conclusion is really compelling, the Impersonal Total Principle should be adopted for impartial comparisons concerning future generations. Nevertheless, where our own interests are affected, we may yet choose to be partial, trading off our concern for future goodness with our self-interests. Theory X' meets all Parfit's requirements except the Mere (...) Addition Principle in less compelling cases. (shrink)