  We present a complete reciprocal description of particle motion inside
multi-component fluids that extends the conventional Onsager formulation of
non-equilibrium transport to systems where the thermodynamic forces are
non-uniform on the colloidal scale. Based on the dynamic length and time scale
separation in suspensions, the particle flux is shown to be related to the
volume-averaged coupling between the Stokes flow tensor and the thermodynamic
force density acting on the fluid. The flux is then expressed in terms of
thermodynamic quantities that can be computed from the interfacial properties
and equation of state of the colloids. Our results correctly describe diffusion
and sedimentation, and suggest that force-free phoretic motion can occur even
in the absence of interfacial interactions, provided that the thermodynamic
gradients are non-uniform at the colloidal surface. In particular, we derive an
explicit hydrodynamic form for the phoretic force resulting from these
non-uniform gradients. The form is validated by the recovery of the Henry
function for electrophoresis and the Ruckenstein term for thermophoresis.
