 Wüthrich (2005, pp. 779–80) has argued that the very existence of approaches to quantum gravity that do not involve the quantization of the gravitational field means that quantization of the gravitational field has to be a contingent matter. However, this seems to rest on a mistake. It might still be the case that there are reasons of logical consistency forbidding the union of a classical and quantum field even though there are entirely distinct non-quantization approaches. For example, string theory does not quantize the gravitational field; however, it is clearly wrong to say that the existence of this position would be ruled out if the various no-go theorems outlawing hybrid classical-quantum theories were true. The fact that one can isolate states corresponding to gravitons in the string spectrum stands quite independent from issues over the interaction of classical and quantum field. The question of the necessity of quantization (as a result of coupling a classical gravitational field to quantum fields) should be held separate from the prospect of producing a quantum theory of gravity that does not involve gravitational field quantization, for both input theories, for describing the classical and quantum fields, could be fundamentally wrong at high energies, requiring entirely new principles. However, a stronger argument against the impossibility hybrids is provided by James Mattingly, who points out that since there are satisfiable axioms for semiclassical theories, inconsistency cannot be established in general (2009, p. 381).