The church fears same-sex marriage because it feels its power waning.

IN RESPONSE to hearing that I am campaigning for marriage equality, an elderly clergyman asked, ''Why call it 'marriage'?'' My response was to outline the huge changes to the institution of marriage that have occurred over the past 150 years.

One hundred and fifty years ago, marriage involved the transfer of property - the bride - from her father to her husband. She was a chattel. Echoes of this persist in some Christian rites of marriage. This is no longer true. Until more recently family bloodlines were viewed as important and certified by marriage. Marriage across racial lines was either illegal or frowned on. Today those interested in bloodlines certify them by paternity tests and racial lines have greatly receded in importance.

While marriage seemed to be very much about family and children in the 1950s that came to an end as the children left home, fertility rates and family size radically declined and the age at first marriage in Australia rose from about 20 to about 30 years of age. Each of these changes reduced the amount of time a couple was likely to spend in child-raising.

One hundred and fifty years ago it was nearly impossible to get a divorce, so desertion was rife and high rates of maternal mortality meant that few couples lived together for a long time. With the receding focus on children, the importance of the quality of the marital relationship became paramount. Where it had declined or disintegrated, divorce came to be not only acceptable but expected. Today more than one-third of marriages involve at least one person who has been married before.

Churches opposed the changes to the divorce law and some still refuse to marry someone who has been divorced. One result of this is that the majority of marriages in Australia are solemnised by civil celebrants, not by the church.

Today marriage has become primarily a matter of companionship between two adults who commit to be there for each other, to build their lives around each other, and to seek the good of the other in an ongoing relationship. Why call this marriage? Many who find themselves in adult companionate relationships seek to do so. Including the elderly clergyman mentioned above who, when well past family and children, had married his current partner.

Today, in Australian society marriage is what we call adult pair-bonding. Even when referred to as ''de facto'' we are actually using a shortened form of the full term ''de facto marriage''. My clergyman would not have accepted this term; why should same-sex people seeking marriage be limited to ''de facto'' status.

When marriage is primarily about adult companionship the gender of those in a relationship ceases to matter. That is what Australians have come to realise.

For some in the church it is all about power. They feel their power waning. They are losing control. The church has already lost the marriage market to civil celebrants. They now face losing the capacity to shape the legal definition of marriage, which is a symbol, not the reality, of their power to coerce Australians to their will. Because this battle is between a group seeking dignity and respect on the one side and another fighting to retain a symbol of its power there is not much ground for rational discussion.

The sociological fact is that the institution of marriage has changed to become one of companionship. This is recognised in Australian law. In this context the gender of partners makes no difference. That is why we should call it ''marriage'' and extend it to all who seek to work together with family and community support to achieve the aims and realise the values of marriage - commitment to care, support, enjoy, love and be there for each other.

Gary Bouma is the author of Being Faithful in Diversity: Religions and Social Policy in Multi-Faith Societies. He is a professor of sociology at Monash University and associate priest at St John's Anglican Parish, East Malvern.

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