  Theoretical description of liquids has been primarily based on the
hydrodynamic approach and its generalization to the solid-like regime. We show
that the same liquid properties can be derived starting from solid-like
equations and generalizing them to account for the hydrodynamic flow. Both
approaches predict propagating shear waves with the notable gap in $k$-space.
This gives an important symmetry of liquids regarding their description. We
subsequently construct a two-field Lagrangian of liquid dynamics where the
dissipative hydrodynamic and solid-like terms are treated on equal footing. The
Lagrangian predicts two gapped waves propagating in opposite space-time
directions. The dissipative and mass terms compete by promoting gaps in
$k$-space and energy, respectively. When bare mass is close to the field
hopping frequency, both gaps close and the dissipative term annihilates the
bare mass.
