Weak pairwise justifiability as a common root of Arrow's and the Gibbard-Satterthwaite theorems

We introduce a novel principle that we call weak pairwise justifiability, which applies to a large class of collective choice rules, including the social choice functions and the social welfare functions about which the Gibbard-Satterthwaite theorem and Arrow's impossibility theorem are predicated, respectively. We prove that, under appropriate qualifications, our principle is a common root for these two classical results, when applied to rules defined over the full domain of weak preference orders (also for strict).