  As Harvey Brown emphasizes in his book Physical Relativity, inertial motion
in general relativity is best understood as a theorem, and not a postulate.
Here I discuss the status of the "conservation condition", which states that
the energy-momentum tensor associated with non-interacting matter is
covariantly divergence-free, in connection with such theorems. I argue that the
conservation condition is best understood as a consequence of the differential
equations governing the evolution of matter in general relativity and many
other theories. I conclude by discussing what it means to posit a certain
spacetime geometry and the relationship between that geometry and the dynamical
properties of matter.
