WHEN Woody Allen parodied the meeting of sperm and egg, everyone knew he was joking. There was Woody, a tiny but fully formed sperm strapped to a parachute and ready to rock. A quick moment of bliss and he was off, launched into a woman's body where he could grow safe and snug.

That's comedy for you - unless of course you happen to be a particular kind of Catholic theologian. Father David O'Hanlon's meteoric rise to celebrity through the pages of this paper and on The Gay Byrne Show is a textbook case of how priests who seem funny can in fact be very dangerous. You suspected the debate wasn't really about costume? You were right.

President Robinson's alleged offence was to wear green, no headdress and a sprig of mimosa at her private audience with Pope John Paul. But when her prosecutor O'Hanlon, a Rome based patristic theology student, mentioned in an aside on radio that women were ontologically different from men, her offence became clearer. The real question is not so much whether she did or did not deliberately flout convention, but rather that she is. She is. That's ontology for you.

Puzzled? Entering the realms of ontology - particularly as practised by the official Catholic Church - involves a very deadly game of theological Dungeons and Dragons, riddled with dummy runs and some 2,000 years of intellectual brinkmanship. Ontology is about being. No more, no less. And until relatively recently, science was its servant.

God made man in His own image, and science backed him up. The ancient Greeks had believed that their gods actually looked human, but Christianity interpreted the resemblance less literally, making it at once more subtle and more powerful.

Human life was sacred, qualitatively different from the beasts in the field because of its spiritual spark. It was man, not woman, who kickstarted the process. Inside a man's seminal fluid was a tiny homunculus, a little Woody Allen, if you like. Women's wombs were incubators, nothing more. The phrase "a bun in the oven" says it all.

THE mistake is easy to understand in retrospect science proceeds by observation and the only visible evidence that sex was a procreative transaction was the man's emission. You could not miss it. Revisionists such as Thomas Aquinas updated some of the clumsy mechanical explanations offered by the early church fathers - "patristic" theologians such as Jerome, Ambrose, or Augustine, now being studied by Father O'Hanlon - but, stuck with the same essential misapprehension.

"God's image is found in man in a way in which it is not found in woman for man is the beginning and end of woman, Just as God is the beginning and end of all creation," wrote Aquinas. He worried about how external forces such as wind direction or water content could determine whether a male or female was conceived.

Aristotle, his mentor, had called the female a "male manque"; patristic theologians such as Gregory had wondered why God made woman, since she was an occasion of sin for man. Why bother in the first place?

Aquinas was inspired. "The human group would have lacked the benefit of order had some of its members not been governed by others who were wiser," he, concluded. "Such is the subjection in which woman is by nature subordinate to man."

Aquinas's teachings were never part of official Catholic faith, according to their leading exponent, the late F.C. Copleston; but in 1879 Pope Leo XIII asserted the permanent value of his synthesis - without correcting its flawed embryological theories.

Pope John Paul's former colleague, the Polish Dominican I.M. Bochenski, called Thomism "the perennial synthesis". Do remember that appointments to many key chairs in Irish universities and hospitals need the approval of the Catholic Church to this day.

So obsessive was the patristic interest in the female, particularly in her body, that men such as Jerome recommended virginity to all women as the only possible solution to their sorry state. Either way, he said, the good woman should surround herself with virgin companions, preferably "pale and thin from fasting". Bride Rosney, take note.

But funny as it may now seem, these bodybased errors were not remedied by science until the discovery of the ovum in 1827, and not addressed by the Catholic Church until the 1970s.

DIDN'T they eventually admit their mistakes? Yes and no. Massive cultural changes, huge social pressure and - not least - a revolution in genetics more or less forced the church to revise its anthropology.

The way was clear for a new discussion about women and about their role in the church - it had made good cultural sense for Jesus to be incarnated in a man's body 2,000 years previously, but the culture had changed, and anyway, science had proved indisputably that women were due the same status in reproduction as were men.

The plot becomes sinister at this point, with the church executing a theological sleight of hand worthy of Houdini.

All of a sudden, maleness was identified not just as a cultural prerequisite for priesthood, but as a divine one too. The evidence offered departed from tradition by introducing a new qualifier, while quoting tradition to justify itself - the same tradition which had been so wrong about biology.

Maleness was now a Christological attribute: it wasn't just the times that were in it which had encouraged a male Christ, but God's own, mysterious, and unarguable order. Patristic ideas about embryology might have been dodgy, but their instincts were correct. Ontologically speaking, men were from Mars and women from Venus. And Mars wins every time.

Thinking like this turned men into donkeys and women into mules. Many theologians considered the new line blasphemous - and still do but the official church silenced them, even though the questions did not always involve dogma.

Separating women and men at an ontological level for ever excluded the possibility of women priests, and degraded the status of priestly men. It was the kind of argument Hitler might have found useful in describing the differences between Aryans and Jews; a question of degree, with one strain clearly of a higher order.

What was Mary Robinson's offence? Just as Jesuit inquisitors always reserved their greatest bile for the good witch, so the President's demeanour is outrageous, if you agree with Father O'Hanlon's ontology. So the mimosa is a symbol of sensitivity, so green is a vivid reminder of nature, so what?

You know her transgression. She is.