Sen (J Polit Econ 78:152–157, 1970) has shown the possible contrast between the social preferences of individuals and their choices. This contrast prevents, in many situations, a social choice that satisfies both Pareto-optimality and liberalism. What liberalism can mean in the field of social choice and the relevance of social organization are briefly discussed. Sen's example, using game theory, determines an equilibrium that is not Pareto-optimal. The contrast between social choice and liberalism discussed by Sen derives from the presence of externalities and happens because it is assumed that individuals are isolated, that is, unable to negotiate with each other to reach a more convenient result for everyone. This paper introduces a kind of negotiation that determines a Pareto-optimal equilibrium if the negotiation is successful. Sen's example leads, using this bargaining process, to a Pareto-optimal equilibrium which is better for both individuals than the Nash equilibrium. This result does not imply that a negotiation always leads to a satisfactory equilibrium. Negotiation can lead to a Pareto-optimal agreement, which, however, is rejected by an individual, as this agreement is no better for him than equilibrium without negotiation, so that Sen’s dilemma reappears.

森（J Polit Econ 78：152–157，1970）表明，个人的社会偏好与他们的选择之间可能存在对比。这种对比在许多情况下阻止了同时满足帕累托最优性和自由主义的社会选择。简要讨论了自由主义在社会选择领域中的含义以及社会组织的相关性。森的例子使用博弈论确定了并非帕累托最优的均衡。森所讨论的社会选择与自由主义之间的对比源于外部性的存在，并且之所以发生，是因为人们假设个人是孤立的，也就是说，彼此之间无法协商，无法为每个人获得更方便的结果。本文介绍了一种协商，如果协商成功，该协商将确定帕累托最优均衡。森 这个例子通过讨价还价过程导致了帕累托最优均衡，这两个个体都比纳什均衡更好。该结果并不意味着谈判总是会导致令人满意的平衡。谈判可以导致帕累托最优协议，但是，该协议却被个人拒绝，因为该协议对他而言并不比没有谈判的均衡更好，因此，森的困境再次出现。