  The correspondence principle made of unitarity, locality and
renormalizability has been very successful in quantum field theory. Among the
other things, it helped us build the standard model. However, it also showed
important limitations. For example, it failed to restrict the gauge group and
the matter sector in a powerful way. After discussing its effectiveness, we
upgrade it to make room for quantum gravity. The unitarity assumption is better
understood, since it allows for the presence of physical particles as well as
fake particles (fakeons). The locality assumption is applied to an interim
classical action, since the true classical action is nonlocal and emerges from
the quantization and a later process of classicization. The renormalizability
assumption is refined to single out the special role of the gauge couplings. We
show that the upgraded principle leads to an essentially unique theory of
quantum gravity. In particular, in four dimensions, a fakeon of spin 2,
together with a scalar field, is able to make the theory renormalizable while
preserving unitarity. We offer an overview of quantum field theories of
particles and fakeons in various dimensions, with and without gravity.
