Catholic dogma doesn't say abortion is always wrong
These are good times for Thomists. Thomism, it's scarcely necessary to tell readers of this newspaper, is the system of theology and philosophy which was developed by the Dominican Thomas Aquinas in the 13th century and which has been hugely influential in Western thinking, particularly in the area of natural law.
For most of the years since, only theologians and philosophers pored over the works of 'the Angelic Doctor', or debated the shifting relevance of Thomistic thought to the changing times.
A glance at the letters pages of the Dublin dailies, however, suggests that Aquinas has been transformed from a dusty old doctor of divinity to a quirky contemporary character.
It is a measure of how large he still looms that advocates and opponents of proposals to bring the law on abortion in the Republic into line with the constitution wrangle over which side in the debate Aquinas would have favoured. His relevance has to do with the idea of ensoulment.
The fundamentalists' argument against abortion arises from a contention that a soul enters every human being at the instant of conception.
It is this - ensoulment - which, in their view, gives a fertilised ovum the same moral status as a sentient adult: it is on this basis that they say that abortion is always wrong, except when necessary to save a separate, equally valuable life.
But is it true that the soul enters the 'body' at the moment of conception? The bad news for the fundamentalists is that this wasn't Aquinas's view at all.
He accepted Aristotle's position that the being in the womb went through three different and distinct stages of development - the vegetative, the animal and, finally, the rational.
It wasn't until the moment of 'quickening' - when the foetus could be felt moving - that the 'rational' soul made its appearance and the foetus acquired human rights.
If this sounds somewhat tangled, then so, for many centuries, was the teaching of the Church, which changed in subtle and sometime unsubtle ways, according to the prejudices, or perceived needs, of this or that pope.
The only pope who declared unequivocally that abortion was wrong from the moment of conception was Sixtus V in 1588. That line lasted three years.
Then Gregory XIV overturned Sixtus's ruling and decreed that abortion became a grave sin only after the foetus was 'animated': Gregory reckoned this happened at 166 days' gestation - 24 weeks, the limit which operates today under the British 1967 Abortion Act.
The years 1588 to 1591 were thus the only period in which the Catholic Church taught what today's pro-lifers want it to teach. Until 1869, that is, when Pius IX announced that, of his 254 predecessors as pope, Sixtus alone had got it right.
Abortion, he decreed, was, after all, just as Sixtus insisted, always wrong and punishable by excommunication.
Pius changed the line, not because of new revelation, or metaphysical insight, but on account of the discovery of how human fertilisation worked.
If the process of development begins at the point when the sperm combines with the ovum, then that's when ensoulment must happen and when abortion must become wrong. (The fact that this amendment to an immutable truth resulted from scientific advance presents a conundrum with which few pro-lifers seem willing to grapple. After all, shouldn't God have known all this already?)
It might also be wondered why, since the teaching appears now to be regarded as enormously significant, it has never been declared infallible.
Perhaps, looking back over the stops and starts and twists and turns in Church thinking, the Vatican cannily decided that maybe this one was a bit too slippery to be tied down for all time.
What's certain is that the contention of pro-lifers that 'abortion is always wrong' does not sit within Christian tradition and is not derived from the dogmatic teaching of the Catholic, or any other Christian denomination.
Its primary utility is now as a political slogan, as a weapon in the continuing culture-war against modernity and rational thought.
We cannot say what side Aquinas would have been on in the abortion debate. We can say that he would have been less than pleased by pro-lifers using his thinking not to sharpen the mind, or as a means towards enlightenment, but as a cudgel with which to clobber their opponents.