  We show that that vector field-based models of the ether generically do not
have a Hamiltonian that is bounded from below in a flat spacetime. We also
demonstrate that these models possess multiple light cones in flat or curved
spacetime, and that the non-lightlike characteristic is associated with an
ether degree of freedom that will tend to form shocks. Since the field
equations (and propagation speed) of this mode is singular when the timelike
component of the ether vector field vanishes, we demonstrate that linearized
analyses about such configurations cannot be trusted to produce robust
approximations to the theory.
