Abstract
Random-field ferromagnetism systems are discussed, using an equivalent annealed system. It is shown how the critical exponents of the random system are related to the exponents of the pure system. The critical exponent eta is expressed in terms of a dimensionality reduction d'=d-2+ eta (d'). The lower critical dimension for the Ising model is two and for the continuous models it is four. Very strong arguments are given for a hyperscaling relation 2- alpha =d'v and for all the exponents to be given by a dimensionality reduction.