Validity of the t-J model

Emery and Reiter [Phys. Rev. B 38, 11 938 (1988)] have questioned the validity of a single-band t-J model to describe the low-energy properties of ${\mathrm{CuO}}_2$ planes. Their criticisms are based on an examination of the exact solution in a ferromagnetic background. In this Comment we present several arguments which lead us to conclude that this ferromagnetic limit however is compatible with the t-J model.