Banning same-sex marriages may not be valid under the constitution

The marriage definition is not so simple. The Commonwealth has power under Section 51 of the Constitution to make laws "with respect to marriage". It may sound bizarre, but a law defining marriage is not a law "with respect to" marriage. Look at it this way: the Constitution sets out the headings.

Interpreting the meaning of those headings is the province of the High Court. Whereas laws under the headings are matters for Parliament. It is for the courts to say whether any law fits under one of the Constitution's headings. "Marriage" is IN the heading, not UNDER the heading.

Take defence, for example. It is a heading. Parliament cannot define defence. Otherwise, Parliament could pass a law saying: "Defence is anything the Minister for Defence says it is and if the Minister wants to lock people up indefinitely because he thinks they are a security risk he can." Such a law would not be a valid law with respect to defence. That much was made clear in the Communist Party case in 1951.

The Australian Constitution is not Through the Looking Glass in which Humpty Dumpty (or John Howard) can say "When I use a word, it means just what I choose it to mean." The words of the Constitution mean what the High Court (not Parliament or the Prime Minister) says they mean.

In 2004 the High Court might well say that "marriage" means the union of two people and not just the union of a man and a woman.

Certainly, in 1901 marriage meant the union of a man and a woman. But the words are not frozen.

Does the word "marriage" in the Constitution denote a relationship between two humans, only one connotation of which is a relationship between a man and a woman? Or does it denote a relationship only between a man and a woman.

If the latter is the case, the Commonwealth could not legislate to recognise gay marriages, even if it wanted to, and its marriage laws could never apply to gay "marriages". That would be left to the states. If the former is the case the Commonwealth's present gender-unspecific legislation would already recognise Australian and foreign gay marriages. The way around it would not be simply to redefine marriage, as Howard suggests; that is constitutionally defective. No, the only constitutionally valid way around it would be to specifically say that all the rights and obligations in the Marriage Act, the Family Law Act and various social security laws apply only to marriages between a man and a woman and not to any other form of marriage. So if legislation is necessary it will have to be directed at gay people, contrary to what Howard says; it will have to specifically exclude them.

A simple definition in the Marriage Act would invite constitutional challenge - which might well be successful under the Communist Party case principles. A bar on recognising foreign gay marriages would probably pass constitutional muster but does not have the political appeal of the simple definition. A bar on applying the rights and duties of marriage to couples unless they are a man and a woman would pass constitutional muster in the event the High Court held the word "marriage" to include gay marriages. But it would be openly discriminatory.

Minefield.