  The stability of the random field Ising model (RFIM) against spin glass (SG)
fluctuations, as investigated by M\'ezard and Young, is naturally expressed via
Legendre transforms, stability being then associated with the non-negativeness
of eigenvalues of the inverse of a generalized SG susceptibility matrix. It is
found that the signal for the occurrence of the SG transition will manifest
itself in free-energy {\sl fluctuations\/} only, and not in the free energy
itself. Eigenvalues of the inverse SG susceptibility matrix is then approached
by the Rayleigh Ritz method which provides an upper bound. Coming from the
paramagnetic phase {\sl on the Curie line,\/} one is able to use a virial-like
relationship generated by scaling the {\sl single\/} unit length $ (D<6; $ in
higher dimension a new length sets in, the inverse momentum cut off).
Instability towards a SG phase being probed on pairs of {\sl distinct\/}
replicas, it follows that, despite the repulsive coupling of the RFIM the
effective pair coupling is {\sl attractive\/} (at least for small values of the
parameter $ g\bar \Delta , $ $ g $ the coupling and $ \bar \Delta $ the
effective random field fluctuation). As a result, \lq\lq bound states\rq\rq\
associated with replica pairs (negative eigenvalues) provide the instability
signature. {\sl Away from the Curie line\/}, the attraction is damped out till
the SG transition line is reached and paramagnetism restored. In $ D<6, $ the
SG transition always precedes the ferromagnetic one, thus the domain in
dimension where standard dimensional reduction would apply (on the Curie line)
shrinks to zero.
