  The pattern speeds of spiral galaxies are closely related to the flow of
material in their disks. Flows that follow the `precessing ellipses' paradigm
(see e.g., Kalnajs 1973) are likely associated with slowly rotating spirals,
which have corotation beyond their end. Such a flow can be secured by material
trapped around stable, elliptical, x_1 periodic orbits precessing as their
Jacobi constant varies. Contrarily, if part of the spiral arms is located at a
corotation region then the spiral structure has to `survive' in chaotic
regions. Barred-spiral systems with a single pattern speed and a bar ending
before, but close to, corotation are candidates for having spirals supported by
stars in chaotic motion. In this work we review the flows we have found in
response models for various types of spiral potentials and indicate the cases,
where order or chaos shapes the observed morphologies.

Astrophysics of Galaxies;Cosmology and Nongalactic Astrophysics