  The response functions for the extended second and third random phase
approximation are compared. A second order perturbation calculation shows that
the first-order amplitude for the direct $3p3h$ excitation from the ground
state cancels with those that are engendered by the $1p1h$-$3p3h$ coupling. As
a consequence nonvanishing $3p3h$ effects to the $1p1h$ response involve off
energy shell renormalization only. On shell $3p3h$ processes are absent.
