  Low-mass disks orbiting a massive body can support "slow" normal modes, in
which the eigenfrequency is much less than the orbital frequency. Slow modes
are lopsided, i.e., the azimuthal wavenumber m=1. We investigate the properties
of slow modes, using softened self-gravity as a simple model for collective
effects in the disk. We employ both the WKB approximation and numerical
solutions of the linear eigenvalue equation. We find that all slow modes are
stable. Discrete slow modes can be divided into two types, which we label
g-modes and p-modes. The g-modes involve long leading and long trailing waves,
have properties determined by the self-gravity of the disk, and are only
present in narrow rings or in disks where the precession rate is dominated by
an external potential. In contrast, the properties of p-modes are determined by
the interplay of self-gravity and other collective effects. P-modes involve
both long and short waves, and in the WKB approximation appear in degenerate
leading/trailing pairs. Disks support a finite number---sometimes zero---of
discrete slow modes, and a continuum of singular modes.
