Nor is it as if our dependency stops there, with our delivery from the womb. Justice Blackmun gives it away: viability is the moment when the foetus is "potentially able to live outside the mother's womb, albeit with artificial aid". In the case of our species, living outside our mother's womb is not the same as standing on our own two feet. Living apart from our mother does not entail achieving independence or living strictly "unaided". It means simply that we might be kept alive by the efforts of others. That a ventilator might work. That intensive care could be lifesaving.

The ancient world was more explicit about an indignation we seem to share. In his Natural History Pliny the Elder commiserated: "But man alone on the day of his birth Nature casts away naked on the naked ground, to burst at once into wailing and weeping, and none among all the animals is more prone to tears, and that immediately at the very beginning of life . . ." It was as if our dependency was a great embarrassment, the secret that could prove the undoing of the species. 

But in our time, importantly, it is feminist philosophers who lead us to contest the basic veracity of viability. Liberal political                    society, writes Seyla Benhabib, should not assume "a strange world" where "individuals are grown up before they have been born". The fantasy of detachment, the illusion of the asocial, the mirage of self-sufficiency — these could only have been sustained in a patriarchal culture which has systematically sidelined the "different voice" of female experience. And, we might add, a culture which involves a good deal of amnesia. For when it comes to abortion I can only insist on autonomy, or on its first flicker that is viability, by forgetting that I — the one now making the decision, the one asserting my independence, the one enjoying my independence — was "of woman born". I can only avoid contradiction by indulging in what Freud termed "the neurotic's family romance" of rejecting his parents.  

All this may seem a far cry from the agony of an unplanned pregnancy, from the lonely moment I have not personally experienced when a woman, or perhaps a couple, wake up, take the test and begin to realise the enormous negative ramifications of that positive result. And nor do I think we can simply turn the clock back, make all abortion illegal, and instantly criminalise tens of thousands of women. But recognising the adoption of viability to have involved a category mistake of profound proportions does raise unsettling questions. It is a state of affairs which is disconcerting, even without bringing in other issues such as late-term abortions on grounds of disability. It does disrupt the neat narratives we tell ourselves about the world we have built since the Second World War. What happens daily on such scale across our hospitals and our clinics, while hundreds of counterpart couples simultaneously in their homes fret about infertility, does complicate our claim to be an ever more serene society. But above all, exposing viability throws us back on the reality of vulnerability and thus the very meaning of human rights.