Defenders of cohabitation portray it as just a more flexible form of marriage. The love is the same as in marriage, they say; all that is missing is "a piece of paper," the marriage certificate. Some see cohabitation as a "trial marriage." They assume that living together will confirm a couple's compatibility and reduce the odds that a subsequent marriage might end in divorce.

Contrasting Relationships

Social science does not support any of these assertions. By every measure, cohabitation is a very different relationship from marriage. Marriages are formed by a series of decisive, publicly announced events: A proposal is made, it is accepted, an engagement is announced, friends and family gather for a wedding, vows and rings are exchanged, and two formerly single persons are declared to be married. By contrast, many couples quietly drift into cohabitation. They gradually spend more time together, one moves his or her possessions piece by piece into the other's residence, one allows his or her lease to expire, and eventually they realize that they are living together full-time.

The two relationships differ dramatically in durability. The average marriage lasts several decades; the average cohabitation, only 15 months. Because their time horizons are longer, married people are much more likely to invest in one another. Husbands and wives almost always pool their assets. They have a single household budget that does not separate "his" and "her" money. They take responsibility for each other's debts and inherit each other's estates.

Cohabitors, by contrast, typically split expenses down the middle. Perhaps as a result of this financial separatism, cohabitors do not tend to save money or accumulate assets at the rate that married people do. Cohabiting men boost their earnings by only half the amount that married men do. There are few mutual legal protections in most cohabitating relationships. A survey showed that only 13 percent of cohabitors have a will, only 10 percent hold property jointly, and only 7 percent have given each other durable powers of attorney for health care decisions.

Cohabitors do not appear to take responsibility for one another's health. Couples who move in together without marrying do not exhibit the same reductions in unhealthy behaviors that married couples do. Cohabitors report levels of physical and mental health in the same range as persons living alone-well below the higher levels of health and happiness reported by married persons.

Sex & Commitment

Cohabitors are particularly vulnerable to one health risk: violence at the hands of their partners. They are three times more likely than married people to report that an argument had become violent during the past year (13 percent versus 4 percent).

Cohabitors are more likely to keep their friends, families, and leisure activities separate. The one thing they do together is have sex. Indeed, cohabitors have sex somewhat more frequently than married couples. But they report less sexual satisfaction. Apparently, the secure commitment of marriage enriches lovemaking, while the provisional nature of cohabitation may induce some "performance anxiety."

Married couples are more sexually faithful. According to the National Sex Survey, cohabiting men are four times more likely than married men to admit having been unfaithful during the past year. The difference for women is even greater: cohabiting women are eight times more likely than married women to have cheated on their partner. (Overall, however, women are less likely to cheat on their partners than men are.)

One reason for these discrepancies may be that the ambiguity of cohabitation leaves wide room for differing interpretations about how exclusive the relationship is. In marriage both spouses know that they have equally vowed to "forsake all others." But in cohabitation there can be a great inequality in the levels of commitment that the two partners bring to the relationship.

Most often, it is the woman who displays the higher level of commitment. Cohabiting women are more likely to believe that the relationship is sexually exclusive and that it is headed toward marriage. Meanwhile, the cohabiting man may have no intention of marrying anytime soon. He may see the woman as a convenient partner for the time being. He is keeping his options open.

Not Conducive to Marriage

There is one category of cohabitation in which the partners more nearly resemble married people in their positive attitudes and behaviors. These are cohabitors with definite plans to marry. But even these couples have not avoided all of the pitfalls of cohabitation. Research shows that the experience of living together raises the risk of divorce by 50 percent.

How do we account for this striking fact? Various explanations have been offered. First, there are "selection effects." That is, cohabitors as a group start out with various characteristics-they are poorer, less educated, less religious, and have a lower view of marriage-that make them less likely to succeed in marriage.

Second, it appears that living together may foster behaviors that are not conducive to a good marriage. Cohabitors, especially serial cohabitors, become accustomed to relationships with limited commitment, limited trust, and limited duration. When disagreements surface, their habit is to dissolve the relationship and move on to the next. It is not so easy to set aside these old patterns of behavior. Living out the total and permanent commitment of marriage may take more work for those who have previously cohabited.

On the other hand, the sexual bond established during cohabitation may render it more difficult for cohabiting couples to make a wise decision about whether they should marry. Having already become "one flesh," first-time cohabiting couples in particular may find it harder to consider the possibility of tearing themselves apart. As opposed to couples that are merely dating, cohabiting couples may be more inclined to ignore the "red flags" warning against an ill-matched marriage.

Cohabitation, it turns out, is not at all a good preparation for marriage.

This column is adapted from "Cohabitation: Marriage Lite or the New Concubinage?", a sidebar to "Is Marriage Worth Defending?", by Alan Wisdom, Mount Nebo Papers, No. 2, Summer 2009, published by the Institute on Religion & Democracy.

Sources Consulted
* Mike McManus and Harriet McManus, Living Together: Myths, Risks, and Answers (Howard Books, 2008).
* Linda J. Waite and Maggie Gallagher, The Case for Marriage: Why Married People Are Happier, Healthier, and Better Off Financially (Broadway Books, 2000.