The (Im)Possibility of a Paretian Rational

We consider situations in which a group takes a collective decision by aggregating individual’s judgments on a set of criteria according to some agreed-upon decision functions. Assuming the criteria and the decision to be binary, we demonstrate that, except when the aggregation rule is dictatorial or the decision rule is particularly simple, such reason-based social choice must violate the Pareto principle at some profile of individual judgments. In the second part of the paper, the normative implications of this impossibility result are discussed. We argue that the normative case for the Pareto Principle is strong in situations of “shared self-interest”, but weak in situations of “shared responsibility”.

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