  During the past decade a number of attempts to formulate a continuum
description of complex states of matter have been proposed to circumvent more
cumbersome many-body and simulation methods. Typically these have been quantum
systems (e.g., electrons) and the resulting phenomenologies collectively often
called "quantum hydrodynamics". However, there is extensive work from the past
based in non-equilibrium statistical mechanics on the microscopic origins of
macroscopic continuum dynamics that has not been exploited in this context.
Although formally exact, its original target was the derivation of
Navier-Stokes hydrodynamics for slowly varying states in space and time. The
objective here is to revisit that work for the present interest in complex
quantum states - possible strong degeneracy, strong coupling, and all
space-time scales. The result is an exact representation of generalized
hydrodynamics suitable for introducing controlled approximations for diverse
specific cases, and for critiquing existing work.
