In this book Cohen examines the role of individual behavior in the philosophy of justice. Cohen starts by telling about his own life as a jewish marxist in Montreal, who later became an analytic philosopher in Oxford. He discusses the core beliefs of marxism with a special emphasis on Marx's views on religion. He argues that marxists have neglected issues of justice and issues of individual behavior. The first was neglected because of wrong views on the working class and the illusion that there would be no real tradeoffs under communism. The second was neglected because of Marx's theory of revolutionary change and history. He finds the missing egaliarian ethos of individual behavior in christianity. Hence the importance of the relationship between marxism and religion.
Cohens next step is to show that Rawls difference principle, which he accepts, must hold for individuals too in a just society. He gives very careful rebuttals of views to the contrary. From this he shows that much less inequality is justified by the difference principle than usually believed.
Now that he handled the case of individual behavior in a just society from a Rawlsian point of view, he adresses the question of how one ought to act in an unjust society. Specifically how should egalitarians act in an unegalitarian society? This leads to the question posed in the title and Cohen spends the rest of the book examining different justifications for why rich people don't have to spend most of their income on ending inequality.
The book will be of interest mainly to marxists and people interested in contemporary political philosophy.