  In this paper we extend the projective symmetry of the full metric-affine
Einstein-Hilbert theory to a new symmetry transformation in the space of affine
connections called the amplified symmetry. We prove that the Lagrangian of the
Standard Model of particle physics is invariant under this new symmetry. We
also show that the gravitational Lagrangian can be modified so that the
amplified symmetry extends to the gravitational sector and hence to the whole
action. The new theory so constructed is shown to be dynamically equivalent to
Einstein-Cartan's though genuinely metric-affine.
