Abstract This paper investigates the emergence of differential object marking (DOM) in the Asia Minor Greek dialect of Pharasa (PhG) under contact with Turkish. We show that DOM in Turkish and PhG are both instances of structural accusative case and DOM can be formally modeled as context sensitive dependent case. We propose that two factors caused the emergence of DOM in PhG, namely (i) case neutralization in indefinite contexts, and (ii) an increase in the number of V-NP idioms borrowed from Turkish where the NP is in bare form. These perturbations led to a significant change in the overall data created by the community resulting in mixed input for the younger generations. Once the amount of bare NPs passed a certain threshold, a divergent grammar became inevitable. We test our proposal using an abductive generalization learning algorithm based on the Tolerance Principle and running a number of simulations. Our simulation results confirm our hypothesis.