 Although welfare economics and concerns about efficiency dominate normative economics, they do not exhaust the subject, and in collaboration with philosophers, economists have made important contributions to contemporary work in ethics and normative social and political philosophy.  Section 5.2  and  Section 5.3  gave some hint of the contributions of social choice theory and game theory. In addition economists and philosophers have worked on the problem of providing a formal characterization of freedom so as to bring tools of economic analysis to bear (Pattanaik and Xu 1990, Sen 1988, 1990, 1991, Carter 1999, Sugden 2018). Others have developed formal characterizations of social welfare functions that prioritize the interests of those who are less well off or that favor equality of resources, opportunity, and outcomes and that separate individual and social responsibility for inequalities (Pazner and Schmeidler 1974, Varian 1974, 1975, Roemer 1986b, 1987, Fleurbaey 1995, 2008, Fleurbaey and Maniquet 2014, Greaves 2015, McCarthy 2015, 2017). John Roemer has put contemporary economic modeling to work to offer precise characterizations of exploitation (1982). Amartya Sen and Martha Nussbaum have not only developed novel interpretations of the proper concerns of normative economics in terms of capabilities (Sen 1992, Nussbaum and Sen 1993, Nussbaum 2000), which Sen has linked to characterizations of egalitarianism and to operational measures of deprivation (1999). There are many lively interactions between normative economics and moral philosophy. See also the entries on  libertarianism,  paternalism,  egalitarianism,  and  economics [normative] and economic justice.