When Pope Francis arrives in Washington this month, he'll be greeted enthusiastically. Among American Catholics, the pope is remarkably popular - 87 percent have a favorable opinion of him - and he's the U.S. church's best chance of overcoming a bad case of spiritual anemia.

But excitement alone cannot heal one of the deepest rifts in Catholic life, not only among American Catholics but worldwide. It has to do with sexuality, although not the priest abuse scandals that have quite properly received attention in recent years. Nothing has divided the church more than its prohibition against contraception, even among married couples.

Approximately 80 percent of U.S. Catholics, including the thoroughly devout, disagree with that stance (support for changing the ruling is nearly as high around the world). And the vast majority ignore the teaching altogether - one study suggests that 68 percent of sexually active American Catholic women have used birth control, sterilization or IUDs.

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Perhaps the fact that so many Catholics shrug off the condemnation tempts church leaders to imagine the question is moot. Aren't there bigger things to think about? Indeed, while Pope Francis has again and again called for a more responsive church, he has shown little interest in revisiting its teaching on contraception. Although he has derided the notion that being Catholic means reproducing "like rabbits," he has praised Humanae Vitae, the 1968 encyclical that reaffirmed the church's birth-control prohibition. At last October's Extraordinary Synod on the Family, bishops grabbed headlines by debating controversial topics such as admitting remarried Catholics to Communion and acknowledging the upsides of same-sex relationships. But the discussion of contraception was perfunctory. The bishops simply called on the church to do a better job of propagating "the message of the encyclical Humanae Vitae." In other words, the widespread rejection of the birth-control ban is simply a messaging problem.

That's not true. The church's unwillingness to grapple with a deep and highly visible gap between official teaching and actual practice undermines Catholic vigor and unity at every level. It encourages Catholics to disregard all manner of other teachings, including those on marriage and abortion. If the church wants to restore its moral authority, it must address this gnawing question.

The church's sexual norms were woven out of the Old Testament, apostolic injunctions and classical doctrines such as Stoicism, which held passion suspect and condemned sexual acts not directed toward procreation as "against nature." But unlike, say, adultery or fornication or defining the conditions of a valid marriage, contraception was a relatively marginal issue until the 20th century, when reliable methods replaced a brew of folk remedies. Before that, birth control was associated with prostitution or illicit sex and decried by virtually all Christian churches. When Anglican churches broke that pattern in 1930, followed by many Protestant denominations, Pope Pius XI reacted with a stern encyclical reasserting the condemnation. Opposition to birth control soon became a kind of identifying mark of Catholicism.

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By mid-century, though, resolve had begun to weaken. The Second Vatican Council had transformed Catholicism, and theologians were stressing the emotional, bonding aspects of marital sex along with the procreative. The emergence of the birth-control pill in 1960 led some theologians to argue that whatever general principles of sexual morality one might draw from human "nature," they did not extend to specific judgments about particular methods and uses of birth control. The faithful seemed to agree - by 1965, 61 percent of U.S. Catholics thought the church would eventually allow contraception.

That was also the thinking of the high-powered Pontifical Commission for the Study of Population, Family and Births, established by Pope John XXIII in 1963 and renewed in 1964 by his successor Pope Paul VI. By late June 1966, an overwhelming majority of the commission - made up mostly of cardinals and bishops, along with theologians, scientists and lay people - concluded that the church should no longer condemn contraception as "intrinsically evil." The commission's recommendation was eventually leaked to the press.

The pope stayed silent, though, for two years. Meanwhile, as scholar Robert McClory wrote, "married couples, unwilling to put their marital lives on hold, made practical decisions on the morality of contraception, more and more often with the approval of priests and bishops." Finally, in July 1968, Pope Paul VI rejected his commission's recommendation. The world's bishops fell in line but with noticeable hemming and hawing. A public protest, signed by more than 600 prominent Catholic scholars, argued that spouses could responsibly decide "according to their conscience" to use artificial birth control.

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Ironically, a handful of conservative prelates and theologians had warned Pope Paul VI that accepting the commission's recommendation would severely damage papal authority which is exactly what happened when he rejected it.

Sociologists, theologians, pastors and bishops have dated a sapping of Catholic confidence in other church teachings about sexuality, and indeed in church authority in general, to the 1968 encyclical. Some researchers have linked frustration over the measure with declines in church attendance, financial contributions and parental support for sons to enter the priesthood. The prominent Catholic theologian Bernard Haring went so far as to write that "no papal teaching document has ever caused such an earthquake in the Church as the encyclical 'Humanae Vitae.' " Many Catholics now disregard the church's teachings on premarital sex, same-sex unions and divorce. According to a recent Pew poll, 70 percent of American Catholics believe it's acceptable for same-sex couples to live together; 86 percent say premarital cohabitation among heterosexual couples is fine. Fewer than half say homosexual behavior or remarriage without annulment is a sin.

Meanwhile, an outspoken conservative minority insists on making opposition to contraception a litmus test for separating "faithful Catholics" from "dissenters," and the past two popes seemed to count it far more than many other qualifications in naming new bishops. In short, the contraception issue has injected paralyzing doses of tension, suspicion, dissemblance and dysfunction throughout Catholic life.

So an American hierarchy that had long campaigned for the "right to health care" gets bogged down in political opposition to the Affordable Care Act. Outstanding Catholic efforts to serve AIDS victims in Africa are discredited by a doctrinaire anti-condom stance in Rome. Advocacy for impoverished families in the Philippines and elsewhere is contradicted by political lobbying against workable birth-control programs.

In October, the church will have a chance to tackle this issue at a follow-up synod, with a somewhat different cast of bishops. Though their final report is not binding, Pope Francis has indicated that he'll take their advice very seriously.

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This time, they should take the opportunity to treat what has been ailing the church since 1968. First, the synod should stop handling Catholics' massive rejection of the birth-control ban as merely a problem requiring more effective church teaching, rather than something requiring more church learning.

Second, they must stop couching the issue of whether married couples should use contraception in vague, elevated code language like "openness to life" or loving "fully" or returning to the "message" of Humanae Vitae. Instead, the synod should acknowledge that the decades of division turn entirely on a handful of sentences in that encyclical. These do not deal with anti-life values or selfish patterns of behavior. Rather they make a very specific judgment about the nature of sexual intercourse: Anything done to prevent conception in any instance whatsoever of intercourse by married couples - regardless of the circumstances, the spouses' intentions or the seriousness of their reasons - is "intrinsically wrong." Is the moral reasoning leading to that unconditional judgment valid? The issue, in other words, is not Humanae Vitae's other insights about married love, the sexual revolution or the potential misuses of humanity's newfound power over reproduction. Nor is it the efficacy or benefits of "natural family planning" (in which sexual intercourse is limited to times of infertility). Nor is the issue the threat of overpopulation or underpopulation, or imposing Western neocolonial values on other cultures. These may be legitimate concerns, but they do not underpin or necessarily lead to Pope Paul VI's fateful ruling.

Obviously, in a three-week session crowded with other topics, the synod cannot resolve a problem festering since 1968. But besides outlining the conflict in clear terms - and perhaps acknowledging the sincerity and moral seriousness of those on both sides - the synod could propose a renewed examination of church teaching on marriage and sexuality, perhaps to mark the 50th anniversary of Humanae Vitae in 2018.

That might involve a rereading of the encyclical in view of its historical context: the disruption of the pill and the sexual revolution combined with anxiety about doctrinal authority in the wake of the Second Vatican Council.

After all, the council itself, by calling for freedom of religion and support for human rights, officially reversed teachings expressed in encyclicals by 19th-century popes traumatized by the French Revolution - teachings that, in ways similar to the treatment of contraception today, many Catholic thinkers and leaders, both clerical and lay, had long been questioning in principle and ignoring in practice.

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But what about Pope Francis, to whom the coming synod will submit its recommendations? One can picture him criticizing contraception as a symptom of the wealthy West's impulse to control nature through technology. One can also imagine that he might prefer to see the condemnation of contraception maintained in principle while bent to the needs of the poor or the burdened in practice. He has not shown himself overly worried about consistency.

It is hard to see, however, how preaching an absolute rule while excusing lots of exceptions could resolve the church's credibility gap or heal its internal division. Too many Catholics would be likely to find that solution not only inconsistent but offensive.

In fact, Pope Francis's most relevant comment about how the upcoming synod should handle this question didn't mention contraception at all. It was the mandate he gave to the bishops at the opening of last year's synod. "Speaking honestly," he insisted, was the their basic responsibility. They should speak their minds "without polite deference, without hesitation." If the church is to speak honestly about a range of pressing sexual issues, the first step will be for its leaders to speak honestly about contraception.

Peter Steinfels is the author of "A People Adrift: The Crisis of the Roman Catholic Church in America" and a former religion correspondent for the New York Times.