  Accounting for elasto-plastic motion in granular media, hypoplasticity is a
state-of-the-art constitutive model derived from data accumulated over many
decades. In contrast, GSH, a hydrodynamic theory, is derived from general
principles of physics, with comparatively few inputs from experiments, yet
sporting an applicability ranging from static stress distribution via
elasto-plastic motion to fast dense flow, including non-uniform ones such as a
shear band. Comparing both theories, we find great similarities for uniform,
slow, elasto-plastic motion. We also find that proportional paths and the
Goldscheider rule used to construct barodesy, another, more recent constitutive
model, are natural results of GSH's equations. This is useful as it gives these
constitutive relations a solid foundation in physics, and in reverse, GSH a
robust connection to reality. The same symbiotic relation exists between GSH
and KCR, or Kamrin's non-local constitutive relation, a model that was
successfully employed to account for a wide shear band in split bottom cells.
