  We consider the quantum evolution of the space-independent mode of a $\lambda
{\phi}^4$ theory as a minisuperspace in the space of all $\phi$. The motion of
the wave packet in the minisuperspace is then compared to the motion of a wave
packet in a larger minisuperspace consisting of the original minisuperspace
plus one space-dependent mode. By comparing the motion of the two packets we
develop criteria that tell us when the quantum evolution in the
space-independent minisuperspace gives us useful information about the true
evolution in the larger minisuperspace. These criteria serve as a toy model for
similar(but much more complex) criteria that will tell us whether or when
quantized gravitational minisuperspaces can possibly give any useful
information about quantum gravity.
