  We argue that Raman scattering in $B_{1g}$ symmetry allows one to distinguish
between phonon-mediated and magnetically-mediated $d-$wave superconductivity.
In spin mediated superconductors, $B_{1g}$ Raman intensity develops a resonance
at a frequency $\omega_{res} < 2\Delta_{max}$, whose origin is similar to a
neutron resonance. In phonon-mediated $d-$wave superconductors, such a
resonance does not develop. Several extensions of the argument are presented.
