Vast moral revolutions do take place once in a while, but it is hard to figure out exactly what sets them into motion or brings them to success. A high-minded prophet in some part of the world denounces an old and dreadful social custom. A smattering of do-gooders plead for reform. The reform in question appears, at a glance, to be impractical, unpopular, and unlikely. And yet enormous masses of people somehow—but how?—end up suddenly embracing the revolutionary idea, and they bend to the task of digging a new foundation for the whole of society. The improbable reform, upon completion, turns out to be irreversible. And in retrospect, absolutely everyone, or nearly so, solemnly agrees that good has, in fact, been done, and moral progress on the grandest of scales is more than a figment of the wistful and naive imagination.

Kwame Anthony Appiah is a philosopher at Princeton, and, in his new book, The Honor Code: How Moral Revolutions Happen, he cites two large and indisputable examples of this strangest and most majestic of historical phenomena. A handful of Quakers organized the earliest anti-slavery committees in America and Britain late in the 18th century. The likelihood of doing away with slavery seemed pretty small, given that plantation slavery in the western hemisphere was proving to be, for entire industries in America and Britain both, an economic bonanza. The slave laborers were suffering horribly, but a lot of other people, not just the plantation owners, were benefiting.

Even so, in England during the 1820s and ‘30s, enormous crowds of earnest and indignant citizens took to attending marathon anti-slavery meetings and affixing their signatures to petitions. Parliament bestirred itself. And, as a matter of law, in 1833 slavery was duly abolished almost everywhere in the worldwide British Empire—one of the hugest, speediest, most peaceful and consequential moral revolutions ever to occur.

Something vaguely similar took place in China in the decades around 1900. For 1,000 years, upper-crust Chinese and not-so-upper-crust Chinese had followed the custom of painfully binding the feet of little girls, and even toddlers, such that when the girls became women, their hobbled feet might turn out to be the size of a man’s thumb. A small group of reformers launched a campaign against the horrible practice. And although Chinese tradition was more than weighty, and although some people found an erotic appeal in deformed feet (Appiah supplies details on the exotic erotica of “the golden lotus,” or the broken and bound feminine foot), the millennial custom descended into obloquy with amazing speed. And then, poof!, it was gone.

Appiah recounts these episodes with a cheerful verve, but he also applies himself, in his capacity as philosopher, to seeking out the hidden mechanisms of persuasion that, in his estimation, drove the campaigns forward. His search leads him to inquire into still another remarkable reform movement from the early 19th century, whose history, as he interprets it, sheds a useful light on the question of moral revolutions as a whole. This was the campaign in England to suppress the aristocratic custom of dueling with pistols.

Appiah reminds us that, as late as 1829, the Duke of Wellington, who was prime minister of Britain, put his life at risk by engaging in an idiotic and illegal duel with a high-born nonentity known as the Earl of Winchelsea. As it happened, the duke’s bullet went awry, and the earl, having survived, chose to aim his own pistol harmlessly in the air. But what would have happened to Britain and its political stability if the prime minister had successfully murdered his man or had ended up murdered himself? In Wellington’s upper ether of the aristocratic world, gentlemen did not worry about such petty things.

Still, dueling came under criticism, and, within a quarter-century, it disappeared altogether, at least in Britain—felled, as Appiah judges it, by a single well-aimed argument. This was not an appeal for rational behavior, or for morality, or law, or Christianity. The fateful argument appealed, instead, to a revised and improved interpretation of aristocratic honor. The very definition of a gentleman, in Cardinal Newman’s formulation, came to be “one of who never inflicts pain”—which could only mean someone who regards dueling as ungentlemanly and even shameful.

Appiah notices a similar formulation cropping up in the anti-slavery campaign. Tradesmen and workers in England began to invoke “the honor of workingmen” as an argument against tolerating slave labor. He notices that still another kind of honor—the “national honor” of China, as seen in the eyes of other countries—played a role in the rhetoric of the anti-foot-binding campaign. Appiah figures that he is on to something. And in his enthusiasm over his discovery, he points to still another such revolution, or potential revolution, that is going on right now.

This is the campaign to condemn and reject the custom, prevalent among the Pashtun population of Pakistan and other groups, too, known as “honor killing”—the murdering of women by members of their own family in order to punish sexual or marital transgressions. Appiah observes that like the anti-dueling, anti-slavery, and anti-foot-binding reformers of the past, some of the campaigners against “honor killing” in our own time have invoked new and improved notions of honor in opposition to the dreadful old practice—the notion, for instance, that violence against defenseless women cannot be regarded as honorable. Appiah applauds this kind of argument. I applaud his applause. Still, I am not convinced of his main point—his contention that reformulated notions of honor have played what he calls a “central role” in the history of moral revolutions.

Dueling faded away for reasons that seem to me easy to identify. Back in feudal times, dueling made logical sense. Aristocrats ruled over everyone else largely through terror and intimidation. By shooting or stabbing one another now and then, the aristocrats reminded themselves and everyone else that aristocrats were scary and tyrannical—the kind of people who, at the drop of a hat, would go about enforcing their whims homicidally, regardless of any objection raised by law, the state, the church, or simple morality. But the feudal age came to an end. In England by the 1830s, the middle class had begun to enjoy a bit of political power, and even toiling proletarians were beginning to mobilize. The state was stronger. There was no point in pretending any longer that violence by irascible titled individuals was likely to keep the rest of society from having its say. And under those circumstances, the anti-dueling moralizers discovered that aristocrats were all too happy to stop threatening one another with guns.

The campaigns against slavery and foot-binding, though—these were much graver affairs, and their progress reflected a much more mysterious and even awe-inspiring historical development, or so it seems to me. The development in question was the gradual acceptance by ever larger populations of the principle of universal human equality. It’s fine and good to observe that orators and polemicists in those campaigns sometimes appealed to the public’s sense of honor. But Appiah’s own account of moral revolutions over the centuries makes me wonder whether something deeper and vaster hasn’t ultimately been driving the grandest of the reform campaigns—something deriving from Christianity, maybe.

Christian evangelizers played the leading role in the anti-slavery movement. A hundred years later, Christian missionaries, as Appiah shows, played a leading role in the Chinese campaign against foot-binding, too—which is odd to consider, given that China has never been Christian. Or maybe, as I prefer to think, an unidentifiable force deeper and older even than Christian doctrine has been at work in these campaigns—a possibility that Appiah himself makes me consider, if only because, in the course of The Honor Code, he refers here and there to the philosopher Hegel, who ruminated at length about moral progress and its spiritual dimensions some 200 years ago.

But this is just to say that I have found Appiah’s book to be wonderfully rich and stimulating. Reading it is like attending a lecture by a lucid and ebullient professor who chuckles over his colorful anecdotes but is ultimately intent on making you think for yourself. Turning the pages, I discover that Appiah is my comrade, too, on a strictly literary matter dear to my own reformer’s heart. This is the modern-day campaign, on which I have been embarked for many years, to rehabilitate the reputation and, as it were, the honor of the exclamation point—a form of punctuation that, for a long time now, has been regarded in respectable publishing circles as a fatal sign of childish naiveté. The exclamation point ought to be regarded, I believe, as a useful tool for expressing the life-affirming quality known as gusto. And Appiah agrees!

He writes, “[I]f your humanity entitles you to respect, then it entitles you to respect even from yourself!” He boasts of having produced his own translations of Sir Thomas Mallory “into modern English!”—all of which seems to me not only admirable, punctuationally speaking, but aptly suited for a treatise on moral revolutions. How can any proper reform campaign hope to succeed, after all, if the intellectual leaders of the campaign refrain from conjuring an enthusiastic mood? And how to conjure enthusiasm, if not by resorting now and then to the wrongly disdained upright exclamation mark? Anyway, Appiah’s Honor Code is an intelligent book that is also, in its enthusiastic professorial style, a charming book.

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