The theory of universals faces two opposing demands. On the one hand, it must be explanatory. That is, certain kinds of statements found in our everyday discourse and the theories used to explain them seem to require the existence of universals for their understanding or acceptance. On the other hand, it must be ontologically appropriate. This means that theories that intervene ontologically without sufficient reasons for the existence of implausible entities or theories that result in an excessive proliferation of new entities should not be embraced as theories of universals.
The problem is that a theoretically sound theory of universals appears to inevitably involve a tension between explanatory and ontological appropriateness. This dilemma arises from the two aforementioned demands, and it is a genuine dilemma in that it is difficult to give up either demand. Philosophy, or metaphysics, fundamentally aims to explain the facts of the experiential world. If a philosophical theory fails to adequately satisfy our explanatory demands regarding the experiential world, it is not suitable as a philosophical theory. Conversely, it is also undesirable for a philosophical theory to impose excessive ontological burdens. The justification of a philosophical theory is a priori, and any a priori claims about the existence of entities should not be arbitrarily adopted.
This article resolves this dilemma as follows: If the explanatory demand requires reduction from an ontological standpoint, it can be adequately addressed through unproblematic means. On the other hand, the apparent conflict between the explanatory demand and appropriate ontology only arises when it is understood as a demand for explanatory priority. However, such a demand does not necessarily require the introduction of any ontological priority. Therefore, there was no need for the dilemma to arise. Finally, I attempt to respond to the demands from natural kind predicates.