Americans seem to be forever undergoing a “crisis” of civility. Year after year, we’re told that the norms dictating decent behavior are eroding; that we’ve lost sight of the basic regard we owe our fellow participants in public life; that the contentiousness of our culture threatens to undermine our democracy. Worrisome stuff, of course — but a little vague. If, as any historian will tell you, people in all times and places have been alarmed by this development (the ancient Romans called it pugna verborum, or “the battle of words”), you might wonder how urgent, or even actual, the trouble really is. Then there’s the problem of definition. One man’s civility is another man’s repression. Were the Act Up protesters in the 1980s so indecorous as to disqualify themselves from political conversation, as their critics charged? Or were they the ones demanding civility, in the form of simple recognition of the lives of people with AIDS? Is Donald Trump dangerously boorish? Or is he, too, resisting an ersatz decorum, one he and his supporters call “political correctness,” which they claim honors the feelings of everyone but the beleaguered white working-class male?

One response to these complexities is to abandon the quest for civility, deeming it a historically fanciful, hopelessly imprecise ideal. Another response, exemplified by the political scientist Keith J. Bybee’s slim and artful treatise HOW CIVILITY WORKS (Stanford Briefs/Stanford University, paper, $12.99), is to suggest we continue to fight for civility but learn to think of it less romantically. Given how nasty and intractable the conflicts in our society can be, Bybee argues, it is naïve to imagine we can somehow transcend our clashing sets of values and miraculously agree on what counts as acceptable behavior and tolerable opinion. After all, if we could find common ground on something as fundamental as that, we wouldn’t have the sort of nasty and intractable conflicts we call on civility to manage in the first place. For better or worse, we must accept that civility “does not exist outside of politics as an independent force,” Bybee writes, but rather is just as much the “subject of political struggle” as everything else.

This solution has a paradoxical cast. The whole point of civility, you might think, is to have a consensus, not on any particular issue of debate, but on the manners that govern disagreement. For Bybee, though, that is a misguided belief. Ultimately, civility is about establishing the rules of “social belonging”: Whose views and interests merit consideration? That is a quintessentially contestable question. Bybee himself favors “more inclusive and egalitarian” conceptions of civility. But there are also hierarchical conceptions that require a social pecking order, like that of Warren Farrell’s men’s rights movement. For Bybee, that broader notions of respect aren’t universal is less a sign of civility’s weakness than a reminder that there is political work to be done.

This view is intended to be hardheaded and unsentimental, but the political theorist Teresa M. Bejan would presumably find Bybee’s conception of civility, rooted as it is in ideas of respect, no less idealistic. In her penetrating and sophisticated study MERE CIVILITY: Disagreement and the Limits of Toleration (Harvard University, $45), Bejan champions an even harder-headed view, that of the 17th-century religious radical Roger Williams. His conception of “mere civility” was based on “mutual contempt” rather than mutual respect. As the founder of the famously inclusive colony of Rhode Island and Providence Plantations, Williams understood firsthand that a tolerant society was not necessarily “a pleasant, harmonious or particularly peaceful place.” He himself tolerated Jews, American Indian “pagans,” Muslims, Catholics and myriad Protestant sects, but not because, like some proto-multiculturalist, he wanted to celebrate or dignify their differences. Instead, Williams worried that if these groups (which “he found most abhorrent”) were excluded from public life and common conversation, he wouldn’t be able to convert them from their strange and filthy ways.

With civility like this, you might ask, who needs rudeness? But the virtue of Williams’s view comes into focus, Bejan contends, when contrasted with those of Thomas Hobbes and John Locke, two other 17th-century thinkers who sought to understand how a tolerant society would work. Hobbes feared that strident expressions of disagreement would threaten the diversity of views in society (much as hate speech is now thought to do), so he advocated an ethic of “civil silence,” or public discretion: People could differ privately in their opinions as much as they wanted but should not openly dispute one another. Locke, by contrast, wanted to preserve public debate, but worried that too much diversity of opinion might jeopardize productive disagreement (the sort of concern campus speech codes now reflect). So he urged an ethic of “mutual charity,” which required people to cultivate at least a minimal appreciation for the views of their opponents, or else be disqualified from debate. Both thinkers, in other words, imagined bringing about a tolerant society via suppression or exclusion — the very forces you would think a tolerant society would want to avoid.

These two influential conceptions of civility survive today in various forms. Their internal tensions help us understand why civility’s critics can always accuse its proponents of their own incivility: Tolerance based on intolerance is a hard trick to pull off. For this reason, Bejan laments that nowadays “Williams’s distinctive voice is nowhere to be found.” His central insight — one that emerged from the hard work of building a diverse community — was that the common ground required to support a tolerant society was much thinner than you might think. Williams asked not that everyone keep quiet or respect his or her enemies, but merely that everyone not do anything to stop the conversation from going. From this perspective, Trump is not uncivil because he is insulting but because he threatens to shut up his opponents. Williams’s “mere civility” demands more of us than Locke’s or Hobbes’s civility, in that it requires we have thicker skins about other people’s rudeness or disrespect; but it also demands less of us, in that we no longer have to muster respect for, or mute our criticism of, views we abhor. For liberals in an age of Trump, that might be a fair trade-off.

If all this hardheaded, disenchanted talk is getting you down, consider the refined and rarefied argument in TOLERANCE AMONG THE VIRTUES (Princeton University, $39.50), by the philosopher and ethicist John R. Bowlin. Whereas Bejan notes with disparagement that Locke’s idea of civility involved “a form of toleration so demanding as to approach a requirement for universal Christian charity,” Bowlin, a seminary professor, would no doubt see that as a point in its favor. Bowlin argues for a “perfectionist account of tolerance,” by which he means to defend it not as a modus vivendi for today’s problems of disagreement and difference, but as a timeless moral virtue. In this, his model is the medieval theologian Thomas Aquinas, who developed a systematic account of many virtues, but not, explicitly, of tolerance. Many of Aquinas’s followers today, Bowlin notes, would resist such an effort, because they think of toleration as “a distinctively modern response” — perhaps even a morally relativistic one — to differences of worldview.

Not only does Bowlin resist this objection, but he also suggests that tolerance is related to the Christian notion of “love’s endurance,” which St. Paul called “forbearance.” To treat the two notions as “sibling virtues,” as Bowlin puts it, is to observe they are deeply similar but also importantly different, so that comparing and contrasting them may serve to illuminate both. Even for non-Christians, Bowlin suggests, “secular theory” about tolerance might “benefit from acquainting itself with theological resources” about love. It’s a unifying thought: Perhaps this, or something like it, was what Barack Obama had in mind at the National Prayer Breakfast in 2010, when he urged that “empowered by faith,” we Americans needed to “find our way back to civility.”