Baker T, Chayes L. On the Unicity of Discontinuous Transitions in the Two-Dimensional Potts and Ashkin-Teller models (43K, amstex) ABSTRACT. We investigate the uniqueness of the discontinuous phase transition of the $q$-state Potts model and the symmetric $q = (s \times s)$ cubic model (generalized Ashkin-Teller model) on the integer square lattice with $q \ge 1$. For the ferromagnetic cases, when there is a discontinuous phase transition we show that the discontinuity can only occur at a point of self--duality.