  We re-examine the semiclassical approximation to quantum gravity in the
canonical formulation, focusing on the definition of a quasiclassical state for
the gravitational field. It is shown that a state with classical correlations
must be a superposition of states of the form $e^{iS}$. In terms of a reduced
phase space formalism, this type of state can be expressed as a coherent
superposition of eigenstates of operators that commute with the constraints and
so correspond to constants of the motion. Contact is made with the usual
semiclassical approximation by showing that a superposition of this kind can be
approximated by a WKB state with an appropriately localised prefactor. A
qualitative analysis is given of the effects of geometry fluctuations, and the
possibility of a breakdown of the semiclassical approximation due to
interference between neighbouring classical trajectories is discussed. It is
shown that a breakdown in the semiclassical approximation can be a coordinate
dependent phenomenon, as has been argued to be the case close to a black hole
horizon.
