We therefore propose to distinguish between the phenomena, that have left distinct traces and are taken as objective indicators for the coherence of the respective period (the identity criterion), and other characteristic phenomena, distinct or not, that are either product of interpretation or that are not directly associated with the coherence of the period as a whole. For instance, “Ming dynasty” is defined by the political system. Any change of our knowledge about the dates of rule of the Ming emperors will change the asserted temporal bounds of “Ming dynasty”. In contrast, Ming porcelain is a good indicator for dating finds from the Ming dynasty. However, change in our knowledge of the dates of production of a certain Ming porcelain style will not affect the temporal bounds of Ming, but at most characterize this style as no more central to Ming etc. In this case, the political system provides the identity criterion, and the porcelain production just a distinct, characteristic phenomenon of this period.