Most people know of couples who are cohabiting. Ten per cent of the population over 18 years of age is cohabiting and more than three-quarters of couples who marry cohabited beforehand, says a 2006 HILDA survey (Household, Income and Labour Dynamics in Australia).

Perhaps none of this should surprise us given the high rates of divorce in recent times and studies that show that children of divorce marry less and divorce more than children raised in intact families. Divorce appears to have introduced increased apprehension and uncertainty where once there was a belief that lifelong commitment was reasonably achievable.

Cohabitation has increased even though many studies have concluded there is a "cohabitation effect" that generally results in poorer marital outcomes. A recent issue of the Australian journal Threshold summarised many of these findings, revealing the risk of divorce increases by 28 per cent when women have two intimate premarital relationships. Premarital cohabitation is also linked with a reduction over time in esteem for marriage and childrearing, poorer communication in marriage, lower levels of marital satisfaction and greater marital domestic aggression.

Perhaps most worrying for women is that premarital cohabitation seems to be associated with lower levels of a husband's dedication. In a 2004 Journal Of Family Issues study more than 900 respondents were asked to rate their agreement with a series of statements assessing their level of dedication to their spouse. After controlling for religiosity, age and income, the level of a man's dedication was found to be "significantly lower in married couples who lived together prior to marriage than in those who did not". The poorer marital outcomes known as "the cohabitation effect" are not simply due to the characteristics of people who choose to cohabit. There appears to be something about cohabitation itself that changes the dispositions and attitudes of people and promotes worse outcomes.

On the face of the most recent evidence it appears that cohabitation is a con. If someone seriously wishes to enhance their chances of lifelong companionship and happiness then one of the clearest ways of doing so is to avoid cohabitation. Living together appears to erode the motivation and commitment that is essential for a successful marriage. In particular, cohabiting makes you more likely to become couple-focused and less likely to value having children.

This has resonances for those many women who cohabit and think this is their best way of eventually marrying and having children. Unfortunately, far too many men continue to believe that there is no requirement for any further formal commitment since those needs they regard as most urgent are already being satisfied. Such men need to realise that they are selling themselves short and letting down their partners very badly.

In contrast to cohabitation and premature sexual intimacy, there certainly seems to be value in those genuine physical expressions of affection which come through that growth in friendship and natural bonding associated with a deepening relationship.

Perhaps we need to rediscover the wonder and value of things such as courtship. There is much to be said for encouraging couples to spend time with one another in a social environment that comprises a range of commonly understood structured rituals. For too many couples, cohabitation seems to "just happen" and they are blissfully unaware of its potential for harm.

We need to construct social frameworks which more clearly signify levels of commitment and get marriage and children more firmly on the agenda. Perhaps every dad should tell his daughter "If your relationship with a bloke starts to get serious make sure that he understands that he is to ask my permission to court you". This does not mean that daughters are their father's property. But such a statement would send a strong signal about what loving a woman means, from the man who has devoted his life to her while she was growing up, to the man who would need to devote his life to her in the future. If nothing else it would give young men a reality check about what is at stake.

Chris Meney is the director of the Life, Marriage and Family Centre for the Catholic Archdiocese of Sydney.