Non-Manipulable Domains for the Borda Count

We characterize the preference domains on which the Borda count satisfies Arrow's ``independence of irrelevant alternatives" condition. Under a weak richness condition, these domains are obtained by fixing one preference ordering and including all its cyclic permutations (``Condorcet cycles"). We then ask on which domains the Borda count is non-manipulable. It turns out that it is non-manipulable on a broader class of domains when combined with appropriately chosen tie-breaking rules. On the other hand, we also prove that the rich domains on which the Borda count is non-manipulable for all possible tie-breaking rules are again the cyclic permutation domains.