  This paper is an application of the ideas of the Born-Oppenheimer (or
slow/fast) approximation in molecular physics and of the Isaacson (or
short-wave) approximation in classical gravity to the canonical quantization of
a perturbed minisuperspace model of the kind examined by Halliwell and Hawking.
Its aim is the clarification of the role of the semiclassical approximation and
the backreaction in such a model. Approximate solutions of the quantum model
are constructed which are not semiclassical, and semiclassical solutions in
which the quantum perturbations are highly excited.
