ジョン・ローマー

Roemer's early work was an attempt to state the main themes of Marxian economics using the tools of general equilibrium and game theory. In Roemer (1982), he proposed a model of agents who were differentiated by their endowments and had to choose occupations—involving either selling labor, hiring labor, or working on one's own capital stock. In optimizing with respect to market prices, agents choose one of five class positions, each consisting of various combinations of these three activities. This gives rise to a class structure, whose agricultural nomenclature would be landlords (who only hire labor), rich peasants (who hire labor and work themselves on their fields), middle peasants (who only work for themselves and do not participate in the labor market), poor peasants (who work on their own plot and sell labor), and landless laborers (who only sell labor). Independently of this taxonomy, individuals are either exploiters or exploited, depending upon whether they consume goods embodying more or less labor than they expend. The central result, the Class Exploitation Correspondence Principle (CECP), states that individuals who optimize by hiring labor are necessarily exploiters, and those who optimize by selling labor are exploited. Thus, a classical Marxian principle, taken as an observed fact in Marx's writings, emerges here as a theorem. Microfoundations are provided for the relationship between exploitation and class.^[2][3]

In simple models (e.g., that of Leontief), the definition of 'labor embodied in goods' is straightforward. With more complicated production sets, it is not, and hence the definition of exploitation is not obvious. Roemer's program was then to propose definitions of embodied labor time, for economies with more general production sets, which would preserve the CECP. This led to the observation that, for general production sets, embodied labor time cannot be defined before one knows equilibrium prices. Thus, contrary to Marx, labor value is not a concept which is more fundamental than prices. Roemer's work is considered one of the seminal works of Analytical marxism.^[2][3]

Roemer's work on exploitation led him to believe that the fundamental cause of exploitation was inequality of ownership of productive assets, rather than the kind of oppression that occurs in the labor process at the point of production—the latter view was held by many in the 'New Left' (see, e.g., Braverman 1974). While writing A General Theory of Exploitation and Class (1982), Roemer met the philosopher G. A. Cohen and the political theorist Jon Elster: they and others became known as the "September Group," encompassing like-minded Marxists, young social scientists and philosophers who saw their task as reconstructing Marxism on solid analytic foundations, using modern techniques. Roemer joined this group in 1981. He was strongly influenced by Cohen, whose work Karl Marx's Theory of History: A Defence (1978) was to become the gold standard of analytical Marxism. Having decided that inequality of asset ownership was the key culprit in capitalist inequality, Roemer, under Cohen's influence, began reading philosophical work on equality.^[2] He was impressed with Ronald Dworkin's (1981a, 1981b) writings, advocating a kind of resource egalitarianism. But in Roemer (1985), he showed that the hypothetical insurance market which Dworkin postulated to take place behind a veil of ignorance did not suffice to compensate those with a poor endowment of natural talents or bad luck in the birth lottery, as Dworkin had intended. In fact, pathologically, Dworkin's insurance market could transfer wealth from disabled to able persons. Influenced as well by Richard Arneson's (1989) proposal, Roemer (1993) proposed a conception of equality of opportunity, which attempted to carry out Dworkin's and Arneson's program—that is, to compensate persons for bad luck in the birth lottery, but to hold them responsible for their choices, or effort. He expanded this theory in Roemer (1996, 1998, 2012), where he proposed an algorithm whereby a society could equalize opportunities for a given objective (wage earning capacity, income, health), consonant with its own view of what factors individuals should be held responsible for, and what factors demanded compensation. Roemer and collaborators have produced a number of applications of this approach (Roemer et al. 2001; Llavador and Roemer 2001; Betts and Roemer 2007; Keane and Roemer 2009; Bjorkund, Jantti, and Roemer 2012). The World Bank (2006, 2009) has employed this approach to evaluate inequality of opportunity in developing countries.

レーマーは当然、「民主主義の階級闘争」、すなわち民主主義社会における階級が互いに利害を争う方法に関心を持っていた。彼は、当時主流だった政治均衡の概念であるホテリング＝ダウンズ均衡にいくつかの理由で不満を抱いていた。第一に、この概念は政治主体が有権者を代表するのではなく、選挙に勝つことだけを気にしていると捉えていること、第二に、均衡は一般的に政策空間が一次元である場合にのみ存在するため、この概念は非常に脆弱であることである。レーマー（1999）は、政党組織が派閥から成り立っているという考えを利用した、政党競争における政治均衡の概念を提案した。この提案のバリエーションの一つでは、各政党組織は3つの派閥から成り立っている。すなわち、党員の平均効用を最大化する政策を提案したい「過激派」、勝利の確率を最大化したい「機会主義者」、そして党員の期待効用を最大化したい「改革派」である。均衡とは、各政党が、その3つの派閥すべての利得を増加させるような別の政策に逸脱できないような政策提案を行うことで成立する。この概念は、政党全会一致ナッシュ均衡（PUNE）と呼ばれ、各政党内の派閥間のナッシュ交渉と政党間のナッシュ均衡を含むものと見なすことができる。PUNEは、政党間の競争で実際に起こっていることを捉えているだけでなく、政策空間の次元に関係なく存在するという利点も持っている。（実際、2つの政党の場合、妥当な条件下では、一般的に2次元の均衡集合または均衡多様体が存在する。）この理論は、Roemer（2001）で拡張され、多くの例に適用された。Roemer、Lee、Van der Straeten（2006）では、この理論を4か国の選挙分析に適用し、政策の2つの次元は税金と移民（または人種問題）であると仮定した。 Roemer（2006）では、動的なモデルが研究され、長期にわたる政治的競争が、民主的に選択された教育財政政策を通じて、より多くの経済的平等を生み出す傾向があるかどうかという問題が提起された。

共同研究者のウンベルト・リャバドールとホアキン・シルベストレとともに、ロエマーは持続可能性の形式理論を練り上げ、それを気候変動の問題に適用した（リャバドール、ロエマー、シルベストレ 2010年および2011年）。^{[ 4 ]}気候変動に取り組む経済学者のほぼ普遍的な慣行である、将来への割引世代効用の合計を最大化するのではなく、著者らは、可能な限り最高のレベルで福祉を維持する、または選択された成長率で福祉の成長を維持する目的を最大化する。ロエマー（2011年）は、割引功利主義的アプローチを批判している。リャバドール、ロエマー、シルベストレ（2012年）では、著者らは、温室効果ガスの排出権の配分をめぐる、グローバル・ノースとグローバル・サウス間の交渉問題をどのように解決できるかを提案している。この提案は、汚染権を国家に予め分配するという倫理的な立場から出発するのではなく、むしろ合意に達するために必要かつ十分であると著者らが主張する、政治的な動機に基づく前提から出発している。

Although evolutionary biologists, anthropologists, and behavioral economists increasingly view Homo sapiens as a cooperative species, almost all of economic theory assumes non-cooperative behavior: general equilibrium theory and non-cooperative game theory are the main tools. Even 'cooperative' game theory does not model cooperation but treats it as a black box: the values of coalitions in a cooperative game are taken as given, and it is not explained how coalitions produce these values. In Roemer and Silvestre (1993), the authors proved the existence, for quite general economic environments, of an allocation they called the proportional solution (PS): an allocation of goods and labor which is Pareto efficient, and in which each receives goods whose value (at supporting efficiency prices) is proportional to the value of their expended labor. In particular, if such an allocation could be realized, it would rectify the inefficiencies exhibited in the Nash equilibrium known as the tragedy of the commons. But how could it be realized? Roemer (1996) showed that the proportional solution is a 'Kantian equilibrium' of a natural game. In Nash equilibrium a player asks, autarkically, whether he can improve his payoff by altering his action, assuming all others' actions remain fixed. In Kantian equilibrium, a player only alters his labor supply by a certain multiple, if he would prefer that all players alter their labor supplies by the same multiple. In other words, he takes an action only if he prefers the situation in which his action is 'universalized.' A Kantian equilibrium is a vector of labor offers such that no player would like to multiply all offers by any non-negative number. This captures a kind of cooperation—agents do not contemplate deviating independently of others, but only in concert with others. In Roemer (2011), it is shown that, in a variety of games, Kantian equilibria deliver Pareto efficient allocations—they rectify the inefficiencies associated with Nash equilibrium. In particular, if a tribe of fishers, who live on a lake, learn to optimize in the Kantian manner, they will use the lake in an efficient manner, avoiding the tragedy of the commons.