Dr Frizzell, who has published this story in the latest issue of the Times Literary Supplement, and I have been emailing each other since the summer. In fact, he did sent me material about the cause of Emma's death - that it wasn't gall stones, but an aortic aneurysm, which I found convincing and did use in the book. When he sent me this paper on his hypothesis about Emma's death being due to syphilis, I simply sent him a note that its was fascinating.

In truth, though, I find it very hard to believe that Emma died of tertiary syphilis. Of course, once can't say for certain - short of digging people up, which, of course, one can't do in the case of Hardy - so, yes, it's conceivable that he contracted the disease as a young man. Once people start concocting theories, you can go on and on. Dr Frizzell supports his case with readings of Hardy's poems, and all the guilt about Emma in those. But you can read anything into Hardy's poetry - and it's very hard to distinguish the fictional from the autobiographical.

But when you have read Hardy, and researched and studied his life and Emma's, and lived with them as you do when you work on a biography, you get a strong sense of who they were. And I just don't think that syphilis was part of the story of Hardy's marriage.

I've done a lot of medical research in the course of working on my biographies, so I'm familiar with the terrain. Jonathan Miller, who is an old friend, once said to me that there is nothing retired doctors [Dr Frizzell is a retired GP] like more than to make posthumous diagnoses. I think there's a lot of truth in that. Dr Frizzell also makes one or two mistakes: he says, for instance, that the estrangement between Thomas Hardy and Emma began in 1891 - but it was nothing like as early as that.

So there is often speculation about the cause of death of a writer - Jane Austen and Katherine Mansfield, for instance. The only perfect subject I've had was Samuel Pepys, and that was because his nephew had an autopsy done on the very day he died, calling in doctors from the Royal Society to perform it and leaving us a marvellous account of it. This was the Enlightenment, of course. But we are rarely so lucky.