Some politicians and some church leaders have busied themselves over Christmas condemning the idea of gay marriage, and using some odd arguments to do so.

For instance, it is said that gay marriage would damage the ‘institution of marriage’.

And a Times editorial replied by arguing that, on the contrary, gay marriage would strengthen that ‘institution’. Now I have been married for nearly 30 years, but bless me if I know what is meant by the ‘institution of marriage’.

When I married my wife, I thought I was forming a lifelong union with her, not entering an institution.

My loyalty is to her, not to a thing (let alone an institution) called marriage.

The idea of marriage has evolved, and it continues to do so.

Today we take it for granted that a marriage must be formally celebrated, whether in a religious or a civil ceremony, but no formality was required in England until 1753.

Until relatively recent times, it was agreed that a wife was subject to her husband, but we have seen a social revolution here.

Few would argue for a return to the days when a husband could sell off his wife at a fair (as happened late into the 19th century).

Until relatively recent times (almost living memory for some of us) it was practically impossible to dissolve a marriage without a great deal of notoriety and expense.

No one wants a marriage to fail, but few of us would want to go back to the days of couples locked into an unhappy marriage for life.

Until relatively recent times, the procreation of children was taken to be the main point of marriage, but today most people recognize the need to balance that with responsible family planning.

A modern marriage, in which a man and a woman regard themselves as equals, in which one or both may have been married before, and in which contraception is used to space and limit the number of children, would frankly have been unrecognisable as a marriage at all a couple of centuries ago.

Those who wish to argue against gay marriage should not rely on arguments about the unchanging character of the ‘institution of marriage’.

If marriage is an ‘institution’ at all, it is one with a built-in faculty for re-inventing itself.