To many conservative Catholics, exemplified by the former High Court judge, Mr Rory O'Hanlon, their church's silence on Ms Celia Larkin's public and political role as the Taoiseach's partner is baffling. And it is, at one level, hard to blame them.
Most people accept that Mr Ahern's private life is his own business. But it is obvious from her extremely prominent role in the official visit of Mr Tony Blair recently that Ms Larkin has emerged from the Taoiseach's private life and taken a position as a public personage.
The Blair visit, and the Taoiseach's official visit to China, on which he was also accompanied by Ms Larkin, marked a definitive crossing of the line between the private and the public. That does not excuse any attempt to pry into the Taoiseach's family life, but it does make it legitimate for citizens to discuss the public meaning of Ms Larkin's position.
You can't, on the one hand, choose to bring a relationship into the arena of formal state business and, on the other, claim that it is a purely private matter.
So it is, in the words of the now famous Church of Ireland Gazette editorial, "remarkable that the Roman Catholic Church, until recently the staunch defender of public morality in this country, has been so silent in this instance". The Catholic Church has, after all, always insisted that marriage is not just a private matter but also a critical public issue.
In his recent interview with Liam Collins in the Sunday Independent, the Catholic Primate, Dr Sean Brady, suggested two reasons for his church's reticence, neither very convincing.
The Church of Ireland Gazette had suggested that such reticence would not have been likely in the days of Archbishop John Charles McQuaid. But, said Dr Brady, "Archbishop McQuaid never condemned anybody publicly".
This must have brought a wry smile to the lips of, for example, John McGahern, sacked from his job as a national school teacher in the Dublin diocese in 1965 for the crimes of writing a banned book and getting married outside the church.
The other reason for silence cited by Dr Brady is that the nature of the relationship between Mr Ahern and Ms Larkin is unclear: "you don't know the circumstances".
Actually, we do. Mr Ahern spoke about them frankly as long ago as the Fianna Fail succession race in 1992, when he went on Pat Kenny's television show and told the State that his marriage had broken down and that he was living with Ms Larkin. He has since spoken about the relationship many times.
If the stated reasons for the church's silence are weak and without conviction, the unstated reasons are strong and serious.
The real reason is that church leaders know what would have to follow a condemnation of the fact that the Taoiseach is conducting a very public relationship with a woman who is not his wife. It would be an insistence that the Taoiseach should give a good example by divorcing his wife and marrying his present partner.
And that, of course, is, from the church's point of view, the greater of two evils.
Far better to pretend that you can't see what's in front of your eyes - that you "don't know the circumstances" - than to see it clearly and draw the inevitable conclusions. In this case, if upholding the institution of marriage is the end, then divorce and remarriage are the only possible means.
What we have in the Ahern-Larkin situation is the result of a peculiar paradox: that divorce was introduced in Ireland too late to save the institution of marriage. For that, the Catholic Church, in both its lay and clerical forms, bears a great deal of responsibility.
To unravel the paradox, we have to start with a simple truth. For most of the life of the State, people had two socially acceptable possibilities: get married or stay single. By the time of the first divorce referendum in 1986, however, the alternatives to marriage were beginning to expand.
As well as homosexuality, or playing the field, they included a new option: cohabitation. In much of Irish society, none of these was as yet respectable but there were, in the cities, large sections of the population willing either to embrace or tolerate them.
What conservatives could never come to terms with was that, in these circumstances, the introduction of divorce (or, more accurately, of the right to remarry) was essentially a conservative demand. It was based on the notion that marriage itself was still an essential institution and that it was cruel and unjust to lock people out of it because their first attempt at it failed.
Conservatives wildly misjudged the situation by persuading themselves that people whose marriages had broken up would, in the absence of divorce, either go back to their husbands or wives or live out their lives in stoic chastity. Instead, of course, most separated people entered new relationships and set up home with new partners.
Ironically, because there was no divorce, mainstream society began to look on cohabiting with increasing sympathy. It went against the grain of decent, conservative Catholics to condemn people for seeking happiness in the aftermath of a failed marriage.
And so, bit by bit, the absence of divorce facilitated the social acceptance of cohabiting. The very word "partner", which intellectual conservatives so abhor, came to be used in polite, conservative society.
By the time divorce was finally introduced, it came too late to have any real effect on public attitudes to the notion of living with a partner other than your spouse. The plain people of Ireland had got used to it. So much so that a substantial majority does not give a damn that the Taoiseach's partner has become, without the benefit of clergy, the effective first lady.
One thing that was obvious during the divorce debates of the 1980s and 1990s was that the church itself had decided that having large numbers of decent people in second relationships was less of an evil than allowing such people to remarry.
Its victory in 1986, though, has proved pyrrhic. It has ended up with what is, from its point of view, the worst of all worlds. We have both divorce and widespread tolerance of second unions outside marriage. By trying to hold the line too long, the church has ended up in a situation where there is no clear line to hold at all.
And the Catholic Hierarchy can't even talk about all of this with any conviction. This is the richest irony of all. Because it allows divorce and remarriage, the Church of Ireland can speak with some authority about the Taoiseach's situation. Because it refuses to countenance divorce, the Catholic Church is condemned to an awkward and shifty silence.