  Abrikosov-Gor'kov (AG) theory, the foundation for understanding pair-breaking
effects in conventional superconductors, is inadequate when there is an
excitation gap (pseudogap) present at the onset of superconductivity. In this
paper we present an extension of AG theory within two important, and
diametrically opposite approaches to the cuprate pseudogap. The effects of
impurities on the pseudogap onset temperature T* and on Tc, along with
comparisons to experiment are addressed.
