This is quite a treat: two books on justice from two of the leading public thinkers in the Anglophone intellectual world. Amartya Sen, the Nobel-prize winning economist, has produced in The Idea of Justice a book that synthesizes half a century of work on choice, rationality and freedom, and provides his first major contribution to political philosophy. Justice, the new volume from superstar Harvard political philosopher Michael Sandel, showcases the thinking on public morality that has made him one of the most sought-after lecturers in the world. It is no surprise that the two books form a discounted “Frequently Bought Together” couple on Amazon. And it is hard to think of a better use of $35.

Sen and Sandel are both left-leaning in political terms. In many, perhaps most, areas of public policy and politics they will be in profound agreement. Both support a socialized health care system; on a recent trip to the United Kingdom, Sen admitted that he remained “mystified” by the American obsession with market-based health provision. Both support equal rights for women, and for lesbians and gays. Both are passionate supporters of public education, particularly greater investment in the education of the most disadvantaged.

But Sen and Sandel arrive at their destinations by radically different routes. Sen is a philosophical liberal in the sense that personal freedom lies at the heart of his philosophy. Sandel is a communitarian, arguing that individuals are defined by and bound into their communities through shared moral codes and obligations. Sandel believes that the answer to the question of “what’s the right thing to do?”–the subtitle of his book–is a collective one. Sen believes each of us must answer it in our own way.

Sandel’s intellectual foundation is the idea of a “common good.” Following robust moral argument, we can collectively decide, for example, that it harms the common good to pay kids to learn to read, allow women to rent out their wombs, permit pornography, or pay mercenaries to fight our wars. It is a sense of a common good that puts what Sandel understands as moral limits on markets. Sen is less interested in limits than in capacities, including the capacity to moralize for oneself. So while he supports quite substantial intervention to provide universal health care, education, equal rights for minorities, and so on, he is less interested in how, in the end, people choose to use their opportunities. Sen wants to set people free by cultivating their capabilities.

The differences might appear modest, but there is a good deal at stake here. Liberal politics, Sandel-style, will take on the cultural right on its own turf, trying to win moral arguments about the common good and then using the political and legal systems to impose it. If liberals follow Sen, on the other hand, they will be more emphatic about providing the capabilities necessary for substantive freedom, but less willing to dictate the terms of their use. A Sandelian liberalism would emphasize measures such as curbs on top pay and profiteering, as well as regulations against inappropriate economic exchanges (for example, paid pregnancy or prostitution). A Sen-inspired creed would focus on investments in health and education for the poorest in society and a strong emphasis on the rights of all individuals and communities to freedom of opinion, lifestyle, and discussion.

Whatever differences there may be in their philosophies, the two men share a similar modus operandi of an energetic pursuit of a profoundly democratic, engaged version of philosophy. They are not content to leave matters to the seminar room. Neither claims to have all the answers or to have constructed a shiny philosophical system to solve all of our dilemmas. Above all, they both believe in the most quintessentially liberal virtue of all: argument.

Sen stands in the intellectual lineage of classical liberalism, from Adam Smith and John Stuart Mill to Leonard Hobhouse and Isaiah Berlin. For him, the true measure of social justice in any society is the “substantive freedoms people enjoy.” This does not mean people should simply be left to their own devices, or that state action and taxation are inimical to freedom. “Substantive” freedom requires that people possess a set of vital “capabilities”–the tools with which they can construct their own life. Education, good health, decent housing, sufficient income, and social capital are all part of what Sen calls the “capability set” of the substantively free citizen. But he insists that how we each make use of our freedom is up to us, and that freedom has value in and of itself. “The freedoms and capabilities we enjoy can also be valuable to us,” he writes. “It is ultimately up to us to decide how to use the freedom we have.”

Sandel, by contrast, is on a search-and-destroy mission against the “moral individualism” that he says underpins liberal philosophy. His book is a call to introduce–or reintroduce–into public debate moral, and even religious, notions of obligation and duty that go far beyond the demands of a liberal society. According to Sandel, the “individualist” view of the world has promoted greed–Wall Street provides him with good material here–selfishness, and a retreat from collective duties. Far from being free agents, people are “encumbered” by social ties and obligations. Sandel’s principal concern is that the liberal insistence on free choice corrodes the social and moral ties that bind communities and societies together: “If we understand ourselves as free and independent selves, unbound by moral ties we haven’t chosen, we can’t make sense of a range of moral and political obligations that we commonly recognize, even prize. These include obligations of solidarity and loyalty, historic memory and religious faith–moral claims that arise from the communities and traditions that shape our identity.”

Sandel doesn’t mention Sen, but he could have picked him as one of those promoting an allegedly “individualistic” view of the world; plenty of other critics have done so. Sen, usually a hugely courteous writer, and generous even to his opponents, gets quite cross about this accusation, which he thinks is usually based on some sloppy thinking. In response to those critics who accuse him of “methodological individualism”–he jokes that “it is not a term of praise”–Sen points out that “people who think, choose, and act” are “a manifest reality in the world.” He concedes that the social and moral norms and ties of communities will influence people, but he insists that “ultimately it is individual valuation on which we have to draw, while recognizing the profound interdependence of the valuations of people who interact with each other.”

This argument is absolutely central to establishing the foundations of progressive politics. Too many people on the left use the term “individualism” as a term of abuse. As Sen says, the fact that we are individuals is a simple, hard fact of social life. This does not prevent us from undertaking moral responsibility for others, or for acting in concert with others to provide social goods, or from engaging in acts of huge, selfless generosity. Mother Teresa, Nelson Mandela, Barack Obama–take your pick. When we say these are remarkable individuals, taking their own choices as individuals, we do not therefore diminish their moral achievements.

Sandel, though, argues that there are moral obligations that simply come with the territory of our lives and over which we do not–or should not–have any choice. He criticizes Sen-type liberals for suggesting that we are “unbound by moral ties we have not chosen.” But in the end, I think that Sandel has to accept that moral ties are “chosen”–while of course being nothing like the choice, say, of which pair of sneakers to buy. People do make a moral choice to “bind” themselves. The fact that the binding is voluntary does not make it somehow less moral. The choice to get married–to choose the “bindings” of matrimony–is surely a deeply moral one, certainly by comparison to being forced into an arranged marriage. Two of Sandel’s own examples help to further illustrate this point: caring for Mom, and bombing your own town.

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.