An important source of legitimacy of collective decisions is their capacity to embody the coherent collective judgements and preferences of a political community – the collective will of a people. If they do not, they risk being meaningless. An important precondition for a coherent collective decision to be reached through majority rule is the existence of a common frame of reference to guide collective decision-making. I point out how dual citizenship could undermine collective rationality inside a community by exposing its citizens to alternative frames of reference guiding the decisions of another political community. Drawing on the psychology of perception I then cast doubt on whether dual citizens will be able to systematically, reliably reformulate their preferences and reconstitute their judgements in line with their two different communities’ frames of reference.