 Note, however, the following: the compartmentalization of theories and their concepts or vocabulary into levels neglects the existence of empirically meaningful and causally explanatory relations between entities or properties at different levels. If they are neglected as theoretical knowledge and left outside as only bridge principles, the possibility of completeness of knowledge is jeopardized.  Maximizing completeness of knowledge here requires a descriptive unity of all phenomena at all levels and anything between these levels. Any bounded region or body of knowledge neglecting such cross-boundary interactions is radically incomplete, and not just confirmationally or evidentially so; we may refer to this problem as the problem of cross-boundary incompleteness as either intra-level or horizontal incompleteness and, on a hierarchy, the problem of inter-level or vertical incompleteness (Kincaid 1997; Cat 1998).