To read the papers or watch the news, one would think that sex and gender are the only issues facing Christians today. Christian thought about war and injustice, or about how to believe in God in this postmodern age, almost never makes the headlines. And the discussion about sex and gender focuses on particular aspects of those issues. Can gay people be ordained? Can a woman be a presiding bishop? Should wives obey their husbands? Such questions seem to arrive in popular debate without much context of Christian thought about sexuality in general, about how we make moral decisions or about what it means to be human. In particular, liberal Christians seem to have no systematic response to the conservative conviction that once we modify traditional sexual mores we begin a slide toward total sexual degradation.

It’s an opportune time, then, for Margaret Farley—Catholic, feminist, Yale faculty member for 35 years and one of the most distinguished theological ethicists in the U.S.—to set out a theory of how to make moral decisions about sex. According to Farley, we needn’t follow all the traditional rules of sexual behavior, but we do need to act justly in love and sex. Her new book explains just what that means.

She presents her theory only after laying careful groundwork. First, she reviews the history of sexual ethics with a discussion ranging from the Bible and the ancient Greeks to the works of Michel Foucault and Catherine MacKinnon. Then she looks at how the sexual customs of other cultures raise questions about our own. Parts of this section seemed to me the weakest in the book—Farley notes the differences but doesn’t always seem to know what we should learn from them.

According to Farley, the basic question of sexual ethics is, “With what kinds of motives, under what kinds of circumstances, in what forms of relationships, do we render our sexual selves to one another in ways that are good, true, right and just?” Just turns out to be the key word. Being just to others means giving them their due—respecting individual differences but treating each individual as of unconditional value.

In just relationships we do no unjust harm (a difficult challenge given how vulnerable people make themselves in sexual relations); we do nothing without the consent of our partner; and we establish relationships based on mutuality and equality. We love in ways that take into consideration the commitments we are making for the future. While not all sexual activity involves producing children, it should take place in a context of responsibility for future generations and a commitment not to harm third parties or forget our wider responsibilities to social justice. These principles provide a middle ground between the traditional rules and “anything goes.”

What do these principles mean in practice? Farley is often quite explicit. Masturbation is OK when it serves relationships rather than burdening them. Use of pornography that weakens our capacity for healthy sexual relations and any kind of sexual abuse or use of power to obtain sex are wrong. Scriptural arguments cited in opposition to homosexuality are misinterpreted, ambiguous or part of a worldview in which the central issue was that men should always be superior to women. In the end there are no good reasons to apply different standards to same-sex and heterosexual relations. Both kinds are good if just, bad if unjust.

Holding marriages together sometimes helps both the partners and their children. But it sometimes allows abuse and misery to continue. Sometimes divorce is better. People who have been married remain related to each other in a variety of ways forever, and that’s one reason to be cautious about remarriage after divorce, but there is no good reason to forbid remarriage in every case.

If all of this sounds contrary to Catholic teaching, Farley may persuade you that Catholic tradition is more commodious than you thought (though it’s interesting that she never mentions abortion).

On a topic about which too many angry polemics are written, Farley’s calm, commonsense style comes as a relief. But it also leads her to avoid direct confrontation. Her footnotes are generally to those who agree with her, and she rarely sets out opposing arguments or offers refutations of them in any detail. This will be a wonderful book to use with students, but those who agree with Farley and then confront critics who have alternative arguments may wish she had given them more ammunition.

It is not hard to feel that our society is really messed up about sex. Teenage boys pressure their girlfriends to “go all the way.” Drunken couples hook up for the night. Divorces leave wounded kids. Does all this imply that we ought to get back to the old rules?

Farley reminds us how many things used to be worse. It was far harder to be gay, far harder to escape an abusive relationship, far harder for women to find equality. The lasting effects of “sexual taboo morality,” Farley writes, “might have to do with developing shame and guilt more than wisdom and prudence about human sexuality.” Young people are pretty good at grasping how justice works in other contexts, so why not encourage them to think about justice with respect to sexuality? “We know the dangers as well as the ineffectiveness of moralism, and the potential dangers of narrowly constituted moral systems and rules. We do not yet know whether an ethic of just love and just sex will transform any young person’s understanding or action. Insofar as we care about our children, it is worth a try.”

I think I agree, but it’s a scary wager to make. Sexual passion is powerful stuff. At least on some occasions an old-fashioned taboo may be a stronger controlling force than a principle of justice. In a society where sex is used to sell nearly everything, young people (and not-so-young people) find living a sexually responsible life really hard. Margaret Farley has the guts and the clarity of mind to give us a third alternative to “narrowly constituted moral systems and rules” on the one hand and sexual chaos on the other. Whether enough people in our society have the good sense and self-discipline to put such a proposal into practice is a harder question.