We propose a method to incorporate pair correlations of an Ising lattice system in molecular 6eld theory
to higher orders. The theory is applied to ferromagnetism, where a system of equations is obtained for the
response function (here the susceptibility). We obtain important corrections on the Weiss model and the
spherical model. This is illustrated by an explicit calculation of the critical temperature and the spurious
phase, appearing for T>Tc near the critical point in the case of a simple cubic lattice.