History and ancestry are sisters, or sisters-in-law. Historians and family historians sit next to each other in archives and public libraries. We take photographs of the same sources; we use the same online repositories and the same digital records. The universe of what is available online has been been shaped far more by the interests of family historians, over the past generation, than by the interests of writers, historians, and history teachers. There is another affinity. It is that history, like family history, is about finding out what really happened. It is about the truth. It can be wrong. The family who are at the centre of my book, An Infinite History, had thirteen children over the period from 1765 to 1783, of whom five were baptised with the name “Jeanne.”

I think I know who was who, and something of what happened to all of them (the oldest Jeanne died in infancy, and the others lived through the French revolution, the Napoleonic wars, and the 19th century economic transformation, dying in 1838, 1852, 1852, and 1860.) But I could be wrong, and so could their grandchildren’s grandchildren’s grandchildren. Only one of the five Jeannes married. If her posterity are looking for her, now, they too could find the wrong sister, or the wrong destiny, or a history which is not true.

Historical fiction is on one side, in this perspective, and history and family history are on the other side, together. The youngest Jeanne, who married an itinerant professor of design, lived with him just outside a maximum-security prison, and was the matriarch of a dynasty of female heiresses, could be the inspiration for a historical novel. It would be a novel, and not a history, or her history.

There is a different sense, all the same, in which history and historical fiction belong together. They are both about imagination, and about how it really was. I wanted to know what happened next, to the family in An Infinite History, and I also wanted to know what their lives were like. Where did they live, and who were their next-door neighbours? What was it like to be there in the small town of Angoulême, during the events of the French revolution that unfolded, as it happened, a few steps from the house in which five of the sisters lived? What was it like during the cholera epidemic of 1855, or when the railway came to Angoulême?

The naturalist novel, for Emile Zola, whose great sequence of novels, the Rougon-Macquart, is also the story of a family in France over five generations, was a “continuous compilation,” an “exact study of facts and things.” Local historians — with whom historians and family historians will also share the reading rooms that are now beginning to reopen, after our own, modern epidemic – are closer, in this respect, to history and to historical fiction. They too, like historians, are interested in the details of the past. Who lived on this street, in 1855, or in this house? What sort of work did they do? Had they moved there from somewhere else, or did they, like the five Jeannes, have relatives who were dispersed around the world?

Historians have many things to discover from family historians about sources and about ingenuity. One of the things that family historians can discover from historians has to do with the varieties of past lives. There are stories to be found, and adventures, romances, and friendships. It is possible to find out who one’s great-great-grandmother was, and also to know something about what she saw out of her window, and who she was close to, among her own brothers and sisters. It is possible, too, to find people who are entirely left out of an ancestry that descends from mother to daughter (or far more often, from father to son.) The oldest of the Jeannes never married, or had children, and she died at the age of 91, a few minutes’ walk from where she was born. But she was the central figure in the extended family, in the sense that she was the only one to become even a little bit prosperous, as a shopkeeper in the town. She and her sisters bought a house, eventually, with a large mortgage, and established a girls’ school on the ramparts in Angoulême. By the mid-nineteenth century, five of her sisters, her brother, her brother-in-law, three of her nieces and two of her great-nieces had moved in with her, or settled next door. This is the view from where they lived.

Angoulême, 1914

One last observation, about the past and the present. An Infinite History begins in 1764 with the grandmother of the thirteen children in Angoulême, and ends in 1906, with the generation of the grandchildren’s grandchildren. I was interested, in the book, in private as well as public memory, and in the connection of conversations — of reminiscing and telling stories — between grandparents (or great-aunts) and their grandchildren. So there was a double link, from the first to the third generation, and from the third to the fifth generation.

But I had a different, more uneasy reason to end the story in the early 20th century. I wanted to avoid the present – to be entirely sure that no one I had written about was alive, or was the mother or father of someone who was alive today. I had the sense, even in respect of individuals who had been dead for more than 200 years, that I was inquiring too much; I wanted not to know about individuals in the present.

Thinking about history and family history, and writing this essay, has made me reconsider. It was fairly easy, with the resources of family history websites, and the public records to which they lead, to find the dates of birth and death of Jeanne’s grand-daughter’s five grandchildren. It took no more than a few minutes, in turn, to find the names of these grandchildren’ own grandchildren – three young men and women living their lives today, somewhere in France.

It was this inquiry that made me understand the distance, despite all the affinities, between history and ancestry. Jeanne Allemand Lavigerie, the Jeanne who married the professor of design, was no more than one out of 128 great-great-great-great-great-great-grandmothers of the three young people in France. I was sure, all the same, that I did not want to trespass on the lives of these individuals in the present by writing their names. An Infinite History is a story, like any historical story, of the vicissitudes of life, and of mobility – and inequality – in space, society, and economic condition. I was uneasy about obtruding this story on individuals of whose own lives it would be a (very small) part. It was history, and nothing more. It was a story, in the end, of the pastness of the past.

Emma Rothschild is the author of An Infinite History: The Story of a Family in France over Three Centuries, published by Princeton University Press.