  It is well known that three-dimensional Einstein's gravity without matter is
topological, i.e. it does not have local propagating degrees of freedom. The
main result of this work is to show that dynamics in the gravitational sector
can be induced by employing the gauge principle on the matter sector. This is
described by a non-dynamical fermion model that supports a global gauge
symmetry. By gauging this symmetry, a vector-spinor field is added to the
original action to preserve the local gauge invariance. By integrating out this
spin-3/2 field, we obtain a gravitational Chern-Simons term that gives rise to
local propagating degrees of freedom in the gravitational sector. This is
defined, after the gauging, by topologically massive gravity.
