  We show that, contrary to common lore, in resonant inelastic x-ray scattering
(RIXS) at the copper L- and M-edge direct spin-flip scattering is in principle
allowed. We demonstrate how this possibility can be exploited to probe the
momentum dependent magnetic properties of cuprates such as the high Tc
superconductors and compute in detail the relevant local and momentum dependent
magnetic scattering amplitudes, which we compare to the elastic and
$dd$-excitation scattering intensities. For cuprates these results put RIXS as
a technique on the same footing as neutron scattering.
