For 45 years, John Casey has been a life fellow of his Cambridge college, Gonville and Caius. He makes it sound like a pretty austere existence: "In the Old Courts, where I live, in winter mine is sometimes the only light."
A certain austerity seems to characterise much of his life.
"I am half-Irish and half-Italian," he says, "so the forms of Catholicism I grew up with were almost different religions. I'm quite interested in the Irish component, because it is splendidly, austerely Augustinian and pessimistic, and totally different from the Italian side."
As he describes in After Lives: A Guide to Heaven, Hell, and Purgatory, Casey was educated in an English day school by Irish Christian Brothers. The headmaster once asked if he was interested in joining the Jesuits. Although he was "pleased to have been asked", and accepted most aspects of Catholic teaching, he considered himself a rationalist and just couldn't accept the validity of the traditional arguments for the existence of God. The result was an anguished crisis of faith.
Casey studied English at King's College, Cambridge, spent a brief period at Harvard University, returned to King's and then moved permanently to Gonville and Caius, five minutes down the road. Straddling the English and philosophy departments, he has lectured on aesthetic criticism, Wagner and tragedy, "the English moralists" (who in Cambridge include Plato and Wittgenstein), Shakespeare, Keats, T.S. Eliot and Joyce.
The last of these is clearly a central figure for Casey and his book opens with an account of the hell sermons Joyce puts into the mouth of Father Arnall in A Portrait of the Artist as a Young Man. These offer a terrifyingly graphic picture of sinners "heaped together in their awful prison, the walls of which are said to be four thousand miles thick: and the damned are so utterly bound and helpless ... that they are not even able to remove from the eye the worm that gnaws it".
Like Joyce, Casey remains haunted by the religion he long left behind. "I stopped practising as a Catholic at the end of my first year in Cambridge," he recalls, "but I've recently returned. I don't think I could have done so unless the Pope had allowed the old liturgy back, because I found the modern one so insipid and banal.
"The church I grew up in was very satisfying spiritually and gave you an intellectual structure that prevented you being a soft liberal - though you might be a Tory or a Marxist - or thinking the latest intellectual fashions were the only things you could possibly believe in. I don't like the assumption that current ideas are eternal.
"But it did in a way make you dysfunctional - it felt like growing up in a ghetto. It was very hard for the Catholic Church to be really part of national life. There was something both emotionally and intellectually limiting about that."
As a counterbalance to his otherwise sheltered life, Casey has travelled a good deal as a journalist - often, it seems, in search of religious intensity. He was "very impressed by both the fervour and the jollity of Friday prayers at the University of Tehran. I find the moral world of Islam a very attractive one."
He was fascinated to discover the authentic voice of "5th-century Christianity, besieged, but with hope drawn from prophecy" among the Copts in Egypt. And, although he had long been a conservative, he found his interest in Catholicism rekindled by spending time among liberation theologians in Nicaragua.
"I got on very well with them," he reports, "and felt some were people of shining character and candour." While they would openly preach to the text "blessed are the poor", they avoided "blessed are the poor in spirit" - since even the bourgeoisie could consider themselves "poor in spirit".
Such experiences made Casey realise that he "very much enjoys talking to extremists". He has visited Hezbollah in Lebanon and - on a tour arranged by Imran Khan, the Pakistani cricketer-turned-politician, who liked what Casey had written about Islam - the madrassa in Pakistan where eight members of the then Taliban Cabinet had been educated.
He soon established a rapport with his hosts when he told them that he thought that "an organisation that bans television and football can't be all bad".
This led to an invitation to Afghanistan and Casey "mentioned a name who was nothing like as famous then, and they said: 'Osama? You'd like to meet bin Laden?'" Back in England, he contacted The Spectator and said he wanted to visit Afghanistan - and his fax "arrived at 10 in the morning of 11 September (2001)! That's where curiosity about extremists can lead you."
Almost all these strands feed into Casey's learned, yet very personal and provocative, "history of the extraordinarily varied ideas people have had about the future life, future punishments for the wicked and bliss for the good".
After Lives takes in the classical world, Egyptians and Israelites, Mesopotamians and Muslims. It pokes fun at the cheap conjuring tricks and "gentle stream of wishful thinking" that characterised the spiritualist movement, even when it provided comfort to despairing parents who had lost sons in the First World War.
And it argues that the efforts of sophisticated theologians to "demythologise" and reinterpret Jesus' virgin birth, resurrection and ascent to heaven represent "an attempt to cling on to the Christian emotions" while refusing to accept the beliefs of most ordinary Christians. Some stories only have "emotional and spiritual power", he argues, when they are "literally understood".
At the heart of the book, however, is an account of the changing Christian doctrines of hell, purgatory and heaven, which find their supreme artistic expression in Dante's Divine Comedy. Casey writes as an ironic but fairly sympathetic chronicler, and claims: "Dante gives you a serious picture of human life, the drama of life, the moral choices one might make. At no point is there a failure of human wisdom."
Any secular humanist is bound to raise a number of objections. Isn't there something corrupting about being encouraged to contemplate the intense and eternal suffering of others, particularly when they are being punished for what now seem like minor misdemeanours? Shouldn't we be appalled by the theologians who envisaged the saved as rejoicing in the suffering of the damned, in some cases even if they were near and dear to them in this life? And hasn't the doctrine of hell often simply made people terrified and miserable?
"I suppose you want me to say: 'this is wicked'," Casey responds, "but I don't know whether I agree that the doctrines of heaven and hell have made people more miserable than they have made them hopeful."
But he does acknowledge that "the idea that sexual sins merit eternal damnation seems to us now not just grotesque but impossible".
Even more revealing is his attitude to "original sin". After Lives sets out the position of St Augustine, John Calvin and others that "human depravity is a universal fact". Casey then goes on to praise the "magnificent logic" of this doctrine and to treat it like an interesting topic for a seminar: "We have to stand back and ask ourselves what the evidence is for this tremendous teaching (apart from Revelation)." Augustine himself points to the greed of babies at the breast and a youthful escapade when he stole some pears from a garden solely because it was forbidden, but these seem an improbable basis for a general claim about ineradicable human wickedness.
More compelling, suggests Casey, is the appalling history of the 20th century, which forces us to face up to something many leading thinkers have been unable to conceive of: "the possibility of unmotivated malice".
"I used to hate Augustine," he says, "but I find that the more I reflect on him, the more I find he is brilliant at seeing the existence of perversity from the baby onwards. I would say that original sin is at least an interesting hypothesis and probably more plausible than a view of human nature that doesn't take account of the origins of perversity. I take it seriously, though I don't say that it's true."
Now 70 (and still teaching), Casey looks back fascinated by the way that "beliefs held almost without question for centuries, and enforced by the authority of venerable institutions, can unpredictably evaporate".
The doctrines of original sin and hell, he believes, "no longer have as powerful a hold on people's imagination", even among committed believers, as they did when he was growing up.
By retaining at least one foot within that world, he often sounds like an anachronism in today's academy. But it also makes him a compelling and challenging guide to the afterlives that have terrified, fascinated and consoled so many generations before us.