The Pareto principle states that if the members of society express the same preference judgement between two options, this judgement is compelling for society. A building block of normative economics and social choice theory, and often borrowed by contemporary political philosophy, the principle has rarely been subjected to philosophical criticism. The paper objects to it on the ground that it applies indifferently to those cases in which the individuals agree both on their expressed preferences and on their reasons for entertaining them, and those cases in which they agree on their expressed preferences while differing on their reasons. The latter are cases of ‘spurious unanimity’, and it is normatively inappropriate, or so the paper argues, to defend unanimity preservation at the social level for such cases: thus the Pareto principle is formulated much too broadly. The objection seems especially powerful when the principle is applied in an ex ante context of uncertainty, in which individuals can disagree on both their probabilities and utilities, and nonetheless agree on their preferences over prospects.
