Marriage has been one of the fundamental organising principles of human society since history began.
But since the nature of marriage is changing in modern times anyway, with people marrying for love and companionship rather than social need, should the traditionally man-and-woman only club admit new members?

What is marriage?

Most people in the West think the answer is pretty obvious:

The voluntary and exclusive union of a man and a woman as husband and wife.
But that excludes same-sex marriage. A more inclusive (but not totally inclusive) definition would be:

The voluntary union of two persons as spouses, to the exclusion of all others.
Same-sex marriage is a big ethical issue in the USA and is sure to become one in the UK too, as more gay people want to honour their partnerships by getting married.

Marriage adds a great deal to a relationship: it gives the parties rights and benefits and a host of supporting mechanisms, and imposes obligations.

Most significantly, it places substantial and formal obstacles in the way of ending the relationship. These obstacles are a vital part of the supporting structure of the relationships.

In marriage the partners are bound by legal bonds into a single married unit, while still retaining the valuable parts of their separate identities.

Historical note

There has never been a time in history when major civilisations or religions granted same-sex relationships the same rights and status as they did to heterosexual marriage.

Although for a period in the 1980s and 90s there was excitement about historical evidence for same-sex marriages (including religious ones) having taken place in the past, the truth of this is now disputed.

Should same-sex couples committed to a long-term and monogamous relationship be allowed to marry?

Why should marriage be regulated at all?

Marriage has been one of the fundamental organising principles of human society since history began. It is important to the future of society because it provides the best social structure within which to bear and raise children.

Most people accept that marriage and family are key institutions in society, and something that it is appropriate for the law to regulate.

In a real sense, there are three partners to every civil marriage: two willing spouses and an approving State.
Marshall CJ, 18 November 2003
And because marriage is thought by many people to be an inseparable part of the nature of the family, the proper rearing of children, the regulating of human relationships and the nature and stability of human society, there is little doubt that it is a suitable area for ethical analysis.

Why is same-sex marriage so topical?

Same-sex marriage has become a live ethical issue in recent decades for several reasons:

same-sex marriage has become legal in some countries - Belgium, Canada and the Netherlands have recently legalised it
civil partnerships are legal in the UK as of December 2005
US court decisions in 2003 suggested that it would soon be legal there - however, elections in 2004 showed that the opponents of gay marriage had not abandoned the fight to stop it
the family laws of many countries now treat same-sex and opposite-sex couples equally, or almost equally
there is no longer a single code of sexual morality
personal freedom of choice is now a significant element in morality
people are now more accepting of different sexualities and see restrictions on consensual adult sexual behaviour as unacceptable
the link between sex and procreation has been weakened by reliable contraception
enjoyment and the expression of affection are just as or more important aims of sex than conceiving children
reproductive technology allows same-sex partners to have children
gay activists have made the issue a priority
court action in Europe and the USA has made discrimination based on sexual orientation illegal