  The one-dimensional harmonic oscillator in a box problem is used to introduce
the concept of a mixed-mode shell-model scheme. The method combines low-lying
``pure mode'' states of a system to achieve a better description in situations
where complete calculations cannot be done and the dynamics is driven by a
combination of modes. The scheme is tested for real nuclei by combining
traditional spherical states, which yield a diagonal representation of the
single-particle interaction, with collective SU(3) configurations that track
deformation. An application to the ds-shell $^{24}$Mg nucleus, using the
realistic two-body interaction of Wildenthal, is explored to test the validity
of the concept. The results shown that the mixed-mode scheme reproduces the
correct binding energy of $^{24}$Mg (within 2% of the exact result) as well as
low-energy configurations that have greater than 90% overlap with exact
solutions in a space that spans less than 10% of the full space. In the
pf-shell, the Kuo-Brown-3 interaction is used to illustrate coherent structures
of the low-lying states of $^{48}$Cr. Alternative basis sets are suggested for
future mixed-mode shell-model studies.
