Sandel suggests that people have a "special responsibility" to care for their own aging mothers, as opposed to randomly selected elderly people. Most people would agree. But where does this responsibility come from? Is it a payback for the love and care they offered in raising us? No: As Sandel points out, most people would still recognize their responsibility, even to a pretty lousy mother. "Insofar as children are obligated to help even bad parents," he writes, "the moral claim may exceed the liberal ethic of reciprocity and consent." But the obligation is comfortably encompassed in the "liberal ethic of consent." It is a moral obligation. And it is up to each of us to shoulder it–but voluntarily. After all, Sandel is not proposing a new law to force people to look after their parents–the Caring for Your Mom Even Though You Don’t Really Like Her Act–or the withdrawal of federal welfare support from elderly people with children who could be supporting them. There are, in fact, some people who abandon and neglect their folks. In most cases, these are not very nice people. But you can’t legislate for niceness.

In the second of Sandel’s examples, a French bomber pilot in World War II is asked to bomb his own village. The pilot knows the raid is important to the goal of defeating the Nazis, but he refuses to carry out the raid himself on the grounds that "he can’t be the one to bomb and kill some of his people, his fellow villagers." Another pilot takes his place. Sandel thinks there is a lesson here: "Is the pilot’s reluctance mere squeamishness or does it reflect something of moral importance? If we admire the pilot, it must be because we see in his stance a recognition of his encumbered identity as a member of his village, and we admire the character his reluctance reflects."

True, we might admire the pilot’s stance. But imagine for a moment he took a different view. Imagine if the pilot, after long and painful reflection, said, "I know this raid has to be carried out to help free France, and the world, from the scourge of the Nazis. I know this cause is even more important than the lives of my fellow villagers; and I know they would agree. So the bombs have to be dropped. And if somebody has to drop them, I should do it. I am not contracting out my moral choice. It is my village, and I want to take responsibility for this. I may be about to kill my own friends, my own neighbors. But the cause of freedom and justice requires it."

What we would think then? I think we might see in his stance a recognition of his encumbered identity as part of the community fighting to rid the world of Nazism. Is his decision to bomb even his own village in the service of this greater cause less or more admirable than a refusal to do so? In this instance, different claims are being made upon the pilot, different "encumbrances" are being weighed in the balance. The critical point is that it is the pilot himself who engages in the moral reasoning required to make this terrible decision and who weighs his responsibilities to his village and nation, and to what Mill called "that wider country, the world."

Who is to say which of these three stances is the morally superior one? There are no easy answers here. I may strongly approve or disapprove of any of these stances; Sandel another; and you, the reader, a third. In a free society, we are at liberty to deeply influence one another–and we do, all the time. But we are not able to impose morality on each other. Sandel is right to say that people do not exist in vacuum, that they are enmeshed in a complex network social relations and moral obligations. But he is wrong to imply that there is an externally generated, unchanged benchmark against which the actions of individuals can be accurately held to moral account.

Sen also probes the moral dilemmas that can arise in situations of war. He describes the reluctance of Arjuna, the great warrior hero of the Sanskrit epic Mahabharata, to fight a terrible battle in defense of his homeland, despite the urgings of duty from Krishna, his charioteer (and, it also turns out, an incarnation of God). Arjuna weighs the loss of life and the fact he’ll have to kill some relatives and insists that he has to take personal responsibility for the consequences of his decision. Arjuna decides it is right to fight, but only after he’s balanced the various competing arguments himself. As Sen puts it, "There is no exemption from personal scrutiny." Although individuals have to make their own decisions, they don’t make them just for their own benefit.

Sen is tackling one of the most dangerous elisions in anti-liberal argument–of "individualism" with the "rational maximisation of utility." People very often make a perfectly rational, reasonable decision to use their capabilities in a way that does not maximize their own utility in any recognizable sense: by caring for an elderly relative, giving their life to helping the neediest in society, or by simple daily acts of kindness. In The Idea of Justice, Sen provides highlights of his previous work, especially in his treatise Rationality and Freedom, criticizing rational choice theory as an idea based on an absurdly narrow view of human motivation. There is a whole branch of behavioral economics, brilliantly summarized in Richard Thaler and Cass Sunstein’s Nudge, showing that even when people do try to rationalize their own utility, they screw it up by discounting time wrongly, miscalculating risk, and giving in to short-term desires over longer-run investments. Sen prefers to think about reasoning rather than rationality. We can choose to give away our own money to a good cause–which must, rationally, lower our utility. But it is a perfectly reasonable decision, made by a free individual whose conception of a good life includes voluntary transfers of money to those in greater need.

It is precisely because the process of valuing different life courses lies with the individual that Sen sets such store by the capabilities of each person. While Sandel supports public health care as an expression of our moral responsibilities to one another within a community, Sen supports public health care because without it millions of Americans will lack the core capability of good health. Unlike Hayek, for whom the term "social justice" was as nonsensical as a "moral stone," Sen does believe in the idea. But for him, the best vision for social justice is a "comparative" one, which examines "what kind of lives people can actually lead." The heroes of the comparative pantheon are Condorcet, Wollstonecraft, and Mill. For them, as for Sen, abolishing slavery, giving women the vote, and attacking hereditary privilege are all blows struck for justice because they free people to lead lives of their own choosing.

Sen’s comparative approach stands in contrast to most modern theories of justice, which are concerned with finding the right rules, institutions, and social contracts for a just society. Rawls remains the pre-eminent contemporary exponent of this school of thought. Sen variously characterizes the proponents of this school as engaged in a "long-range search for perfectly just institutions," a hunt for "spotless justice" and "transcendental identification of the ideal institutions." The political problem with this is that the search for a perfect set of arrangements for society can distract us from tackling real-life, immediate injustices. In political philosophy, the perfect quickly becomes the enemy of the good.

In most contemporary political arguments, Sen and Sandel will be brothers-in-arms. The difference lies in their competing visions of a good society–for Sandel it is one where a mostly settled view of the common good has been arrived at; for Sen, it is one full of capable, responsible individuals arguing and disagreeing about the best way to live. For my money, Sen’s is the approach with more mileage.

But Sandel, as much as Sen, is a public intellectual in the best sense of the term, impatient for a better world. Political philosophy is an activity which is mostly conducted in a semi-clandestine manner in the remote locations of Ivy League lecture rooms. Not for these two. Sen and Sandel argue for and exemplify a deliberative democracy, resting not on the occasional vote but on ongoing engagement and argument. "There is no chance," Sen writes, "of resting the matter in the ‘safe’ hands of purely institutional virtuosity. The working of democratic institutions, like that of all other institutions, depends on the activities of human agents."

Sandel likewise insists that "to achieve a just society we have to reason together about the meaning of the good life, and to create a public culture hospitable to the disagreements that will inevitably arise." He concludes his relevant volume with a call for "a more robust public engagement with our moral disagreements."

When Sen gave a lecture at Oxford at the end of 2009, the demand to hear him was so great that the chancellor flung open the doors of the Sheldonian Theatre, in defiance of fire regulations, to let in the hundreds outside who had failed to secure a seat but were willing to sit on the floor. Responding to a question about his close friend, the ex-Marxist moral philosopher Gerry Cohen, who died last year, Sen said that Cohen had been a "romantic about theory," while Sen himself had resisted the attractions of purely theoretical philosophy. He was asked why. The 76-year-old replied with great force. "Because," he said, thumping the lectern, "there are things to be done!" Indeed there are.