西方传统中，社会契约理论是最强大的社会正义理论之一，罗尔斯的正义论在当代首屈一指，但它也未能解决如下三个社会正义问题：我们如何把教育、健康关怀、政治权利和自由等这些平等的公民权利延伸到那些身体和心理不健全者？我们如何把正义和有尊严的生活条件延伸到世界上的所有公民？我们如何把非人类动物纳入我们的社会正义观？
玛莎•C•纳斯鲍姆的杰出著作《正义的前沿》，正是从处理这三个长期被现存理论所忽视的、亟待解决的社会正义问题入手，寻求一种可以更好地指引我们进行社会合作的社会正义理论。基于对现有社会契约理论在这三个方面局限性的反思，纳斯鲍姆发展出一种基于“能力”的替代理论，这一理论有助于我们更清楚地思考政治合作的目的和政治原则的本质，以及期待一种适应于所有物种包括非人类动物的更大正义。

Theories of social justice are necessarily abstract, reaching beyond the particular and the immediate to the general and the timeless. Yet such theories, addressing the world and its problems, must respond to the real and changing dilemmas of the day. A brilliant work of practical philosophy, "Frontiers of Justice" is dedicated to this proposition. Taking up three urgent problems of social justice neglected by current theories and thus harder to tackle in practical terms and everyday life, Martha Nussbaum seeks a theory of social justice that can guide us to a richer, more responsive approach to social cooperation. The idea of the social contract--especially as developed in the work of John Rawls--is one of the most powerful approaches to social justice in the Western tradition. But as Nussbaum demonstrates, even Rawls's theory, suggesting a contract for mutual advantage among approximate equals, cannot address questions of social justice posed by unequal parties. How, for instance, can we extend the equal rights of citizenship--education, health care, political rights and liberties--to those with physical and mental disabilities? How can we extend justice and dignified life conditions to all citizens of the world? And how, finally, can we bring our treatment of nonhuman animals into our notions of social justice? Exploring the limitations of the social contract in these three areas, Nussbaum devises an alternative theory based on the idea of "capabilities." She helps us to think more clearly about the purposes of political cooperation and the nature of political principles--and to look to a future of greater justice for all.