05/12/2012 11:07 GMT | Updated 04/02/2013 05:12 GMT

The Royal Glass Ceiling: Why Can't Women be Kings?

If Wills and Kate have a daughter, we are told, she will inherit the throne, even if she should later get a younger brother. In other words, the line of succession will become gender-blind.

Many royal houses have made this move in recent decades, but none of them have achieved true gender equality - none of them have systems in which women genuinely are equal to men. And unfortunately, the Commonwealth will do no better.

A woman still cannot reach the pinnacle of a monarchy - a woman, so to speak, cannot become king!

The limitations that persist become clear through the titles emerging from marriage.

If an heir to the throne marries, their new spouse can get a comparable title. Prince Haakon of Norway married Mette-Marit Tjessem Høiby and she became Princess Mette-Marit. Princess Victoria of Sweden married Olof Daniel Westling and he became Prince Daniel.

When Haakon becomes King of Norway, Mette-Marit will become Queen. But when Victoria becomes Queen of Sweden, Daniel will not become King; instead, he will remain a prince.

Or, to be more precise, both will become Consort to the Regent. Mette-Marit will be the Queen Consort, as is her mother-in-law, Sonja. Daniel will not be a King Consort, but instead a Prince Consort, like Henrik of Denmark.

Why is this? The answer seems clear and simple. Monarchies codify the superiority of a man to a woman. A king always outranks a queen - a man always outranks a woman. The highest position in a royal house may never be occupied by a woman because the highest position is that of king, which is reserved for a man.

When a princess-by-marriage becomes a queen, that creates no confusion regarding the legal position of her husband, the king. But a man who has married a princess cannot become a king, lest we become uncertain about who is really in charge.

A woman who is heir-to-the-throne does not ascend to the highest position in the monarchy. But when she becomes Queen, the highest position - that of King - is kept vacant.

The monarchies in this way, systematise deeply sexist and discriminatory perspectives on the relative value of men and women.

If the Scandinavians or the Brits want to do something truly egalitarian, they would not only let women inherit the throne, they would let their husbands become King, and nonetheless insist that the Queen is at the top of the heap.

But this is perhaps too much to expect of such venerable institutions. On the matter of royal sexism, it's perhaps easier to simply chuckle and conclude: We are quite amused.