Cognitive Warfare is gaining ground in the strategic and operational debate. Accordingly, there are various calls for the introduction of a cognitive domain. The partitioning of warfare into operational domains within the framework of Multi-Domain Operations (MDO) effectively reduces the complexity of military decision models as long as the majority of dependencies occur within the individual domains and the interactions between the domains are limited. Using general model theory, we attempt to show that this is not the case when a cognitive domain is added to MDO. Cognitive Warfare is so strongly intertwined with other domains that it does not represent an independent partial model and, therefore, cannot be contained as an independent domain but must be considered within the generally accepted domains.