 Cao (2001) believes that the conceptual nature of the problem demands a conceptual resolution. He advocates what he calls ‘ontological synthesis’. This approach asks for an analysis of the ontological pictures of the two ingredient theories of quantum gravity, so that their consistency (the consistency of the resulting synthesis) can be properly assessed. Ontology for Cao refers to the primary, autonomous structures from which all other properties and relations in a theory are constructed. A fairly simple inspection of the respective ontological constraints imposed by general relativity and quantum field theory reveals serious tension: general relativity discards the fixed kinematical structure of spacetime, so that localization is rendered relational, but in quantum field theory a fixed flat background is part of its ontological basis, from which the standard features of the theory are derived. On the other hand, as we have seen, quantum field theory involves quantum fluctuations in the vicinity of a point, while general relativity involves the use of a smooth point neighbourhood. Either way, in order to bring the two ontological bases together, some piece of either edifice must be demolished. Cao proposes that the tension can best be resolved by focussing firmly on those sine qua non principles of the respective theories. Cao views the gravitational property of universal coupling as essential, but notes that this does not require continuity, so that the former could be retained while discarding the latter, without rendering the framework inconsistent, thus allowing for quantum theory’s violent fluctuations (Cao’s prime candidate for an essential quantum field theoretic concept). Likewise, he argues that quantum field theory requires a fixed background in order to localize quantum fields and set up causal structure. But he notes that a relational account of localization could perform such a function, with fields localized relative to each other. In so doing, one could envisage a diffeomorphism covariant quantum field theory (i.e. one that does not involve reference to fields localized at points of the spacetime manifold). The resulting synthesized entity (a violently fluctuating, universally coupled quantum gravitational field) would then be what a quantum theory of gravity ought to describe.