In 2006, i was 50—and I was falling apart.

Until then, I had always known exactly who I was: an exceptionally fortunate and happy woman, full of irrational exuberance and everyday joy.

I knew who I was professionally. When I was 16, I’d discovered cognitive science and analytic philosophy, and knew at once that I wanted the tough-minded, rigorous, intellectual life they could offer me. I’d gotten my doctorate at 25 and had gone on to become a professor of psychology and philosophy at UC Berkeley.

I knew who I was personally, too. For one thing, I liked men. I was never pretty, but the heterosexual dance of attraction and flirtation had always been an important part of my life, a background thrum that brightened and sharpened all the rest. My closest friends and colleagues had all been men.

More than anything, though, I was a mother. I’d had a son at 23, and then two more in the years that followed. For me, raising children had been the most intellectually interesting and morally profound of experiences, and the happiest. I’d had a long marriage, with a good man who was as involved with our children as I was. Our youngest son was on his way to college.

I’d been able to combine these different roles, another piece of good fortune. My life’s work had been to demonstrate the scientific and philosophical importance of children, and I kept a playpen in my office long after my children had outgrown it. Children had been the center of my life and my work—the foundation of my identity.

And then, suddenly, I had no idea who I was at all.

My children had grown up, my marriage had unraveled, and I decided to leave. I moved out of the big, professorial home where I had raised my children, and rented a room in a crumbling old house. I was living alone for the first time, full of guilt and anxiety, hope and excitement.

I fell in love—with a woman, much to my surprise—and we talked about starting a new life together. And then my lover ended it.

Joy vanished. Grief took its place. I’d chosen my new room for its faded grandeur: black-oak beams and paneling, a sooty brick fireplace in lieu of central heating. But I hadn’t realized just how dark and cold the room would be during the rainy Northern California winter. I forced myself to eat the way I had once coaxed my children (“just three more bites”), but I still lost 20 pounds in two months. I measured each day by how many hours had gone by since the last crying jag (“There now, no meltdowns since 11 this morning”).

I couldn’t work. The dissolution of my own family made the very thought of children unbearable. I had won a multimillion-dollar grant to investigate computational models of children’s learning and had signed a contract to write a book on the philosophy of childhood, but I couldn’t pass a playground without tears, let alone design an experiment for 3-year-olds or write about the moral significance of parental love.

Everything that had defined me was gone. I was no longer a scientist or a philosopher or a wife or a mother or a lover.

My doctors prescribed Prozac, yoga, and meditation. I hated Prozac. I was terrible at yoga. But meditation seemed to help, and it was interesting, at least. In fact, researching meditation seemed to help as much as actually doing it. Where did it come from? Why did it work?

I had always been curious about Buddhism, although, as a committed atheist, I was suspicious of anything religious. And turning 50 and becoming bisexual and Buddhist did seem far too predictable—a sort of Berkeley bat mitzvah, a standard rite of passage for aging Jewish academic women in Northern California. But still, I began to read Buddhist philosophy.

In 1734, in scotland, a 23-year-old was falling apart.

As a teenager, he’d thought he had glimpsed a new way of thinking and living, and ever since, he’d been trying to work it out and convey it to others in a great book. The effort was literally driving him mad. His heart raced and his stomach churned. He couldn’t concentrate. Most of all, he just couldn’t get himself to write his book. His doctors diagnosed vapors, weak spirits, and “the Disease of the Learned.” Today, with different terminology but no more insight, we would say he was suffering from anxiety and depression. The doctors told him not to read so much and prescribed antihysteric pills, horseback riding, and claret—the Prozac, yoga, and meditation of their day.

The young man’s name was David Hume. Somehow, during the next three years, he managed not only to recover but also, remarkably, to write his book. Even more remarkably, it turned out to be one of the greatest books in the history of philosophy: A Treatise of Human Nature.

In his Treatise, Hume rejected the traditional religious and philosophical accounts of human nature. Instead, he took Newton as a model and announced a new science of the mind, based on observation and experiment. That new science led him to radical new conclusions. He argued that there was no soul, no coherent self, no “I.” “When I enter most intimately into what I call myself,” he wrote in the Treatise, “I always stumble on some particular perception or other, of heat or cold, light or shade, love or hatred, pain or pleasure. I never can catch myself at any time without a perception, and never can observe any thing but the perception.”

Hume had always been one of my heroes. I had known and loved his work since I was an undergraduate. In my own scientific papers I’d argued, like Hume, that the coherent self is an illusion. My research had convinced me that our selves are something we construct, not something we discover. I had found that when we are children, we don’t connect the “I” of the present to the “I” of the past and the future. We learn to be who we are.

Until Hume, philosophers had searched for metaphysical foundations supporting our ordinary experience, an omnipotent God or a transcendent reality outside our minds. But Hume undermined all that. When you really look hard at everything we think we know, he argued, the foundations crumble. Descartes at least had said you always know that you yourself exist (“I think, therefore I am”), but Hume rejected even that premise.


Hume articulates a thoroughgoing, vertiginous, existential kind of doubt. In the Treatise, he reports that when he first confronted those doubts himself he was terrified—“affrighted and confounded.” They made him feel like “some strange uncouth monster.” No wonder he turned to the doctors.

But here’s Hume’s really great idea: Ultimately, the metaphysical foundations don’t matter. Experience is enough all by itself. What do you lose when you give up God or “reality” or even “I”? The moon is still just as bright; you can still predict that a falling glass will break, and you can still act to catch it; you can still feel compassion for the suffering of others. Science and work and morality remain intact. Go back to your backgammon game after your skeptical crisis, Hume wrote, and it will be exactly the same game.

In fact, if you let yourself think this way, your life might actually get better. Give up the prospect of life after death, and you will finally really appreciate life before it. Give up metaphysics, and you can concentrate on physics. Give up the idea of your precious, unique, irreplaceable self, and you might actually be more sympathetic to other people.

How did Hume come up with these ideas, so profoundly at odds with the Western philosophy and religion of his day? What turned the neurotic Presbyterian teenager into the great founder of the European Enlightenment?

In my shabby room, as I read Buddhist philosophy, I began to notice something that others had noticed before me. Some of the ideas in Buddhist philosophy sounded a lot like what I had read in Hume’s Treatise. But this was crazy. Surely in the 1730s, few people in Europe knew about Buddhist philosophy.

Still, as I read, I kept finding parallels. The Buddha doubted the existence of an omnipotent, benevolent God. In his doctrine of “emptiness,” he suggested that we have no real evidence for the existence of the outside world. He said that our sense of self is an illusion, too. The Buddhist sage Nagasena elaborated on this idea. The self, he said, is like a chariot. A chariot has no transcendent essence; it’s just a collection of wheels and frame and handle. Similarly, the self has no transcendent essence; it’s just a collection of perceptions and emotions.

“I never can catch myself at any time without a perception.”

That sure sounded like Buddhist philosophy to me—except, of course, that Hume couldn’t have known anything about Buddhist philosophy.

Or could he have?

I settled into a new routine. Instead of going to therapy, I haunted the theology sections of used-book stores and spent the solitary evenings reading. I would sit in front of my grand fireplace, where a single sawdust log smoldered, wrapped in several duvets, and learn more about Buddhism.

I discovered that at least one person in Europe in the 1730s not only knew about Buddhism but had studied Buddhist philosophy for years. His name was Ippolito Desideri, and he had been a Jesuit missionary in Tibet. In 1728, just before Hume began the Treatise, Desideri finished his book, the most complete and accurate European account of Buddhist philosophy to be written until the 20th century. The catch was that it wasn’t published. No Catholic missionary could publish anything without the approval of the Vatican—and officials there had declared that Desideri’s book could not be printed. The manuscript disappeared into the Church’s archives.

I still couldn’t think or write about children, but maybe I could write an essay about Hume and Buddhism and include Desideri as a sort of close call—a missed connection.

I consulted Ernest Mossner’s classic biography of Hume. When Hume wrote the Treatise, he was living in a little French town called La Flèche, 160 miles southwest of Paris. Mossner said Hume went to La Flèche to “rusticate,” probably because it was cheap. But he also mentioned that La Flèche was home to the Jesuit Royal College.

So Hume lived near a French Jesuit college when he wrote the Treatise. This was an intriguing coincidence for my essay. But it didn’t really connect him to Desideri, of course, who had lived in Rome and Tibet.

When I searched the library databases at Berkeley, I found hundreds of books and thousands of articles I could read about David Hume, but only two about Ippolito Desideri: one article and a drastically abridged 1932 English translation of his manuscript. The article had appeared in Indica, an obscure journal published in Bombay, in 1986. I had to get it shipped down from the regional storage facility, where millions of books and articles in Berkeley’s collection languish unread. Ever since my love affair had ended, I had gone to bed each night dreading the next day. But now I found myself actually looking forward to tomorrow, when the article would arrive.

It mostly recapitulated what I had read before. But the author, an Italian named Luciano Petech, mentioned that he had edited a 1952 collection of missionary documents, I Missionari Italiani nel Tibet e nel Nepal, and that it included some Desideri manuscripts. And, in passing, he provided me with an interesting new detail. “In January 1727,” Petech wrote, “he left India, once more on a French ship, and arrived in Paris.”

Desideri had come back to Rome through France—one more intriguing coincidence.

The abridged Desideri translation could be read only in the Rare Book Room, so I headed there the next day. It was a beautiful book with red capital letters and romantic tipped-in photographs of majestic Buddhas and tranquil Himalayan valleys. I began to read eagerly.

I had been obsessively, ruminatively, fruitlessly trying to figure out who I was and what I would do without work or love or children to care for. It was like formulating an argument when the premises refuse to yield the conclusion, or analyzing a data set that makes no sense. But if I couldn’t figure myself out, I decided, I could at least try to figure out Desideri, and so I lost myself in his book, and his life.

It’s a remarkable story. In his 20s, Desideri conceived his own grand project—to convert the Indies to Catholicism—and in 1716 he became one of the first Europeans to go to Lhasa, and the first to stay. He was passionate, emotional, and easily exasperated. He was also curious, brave, and unbelievably tenacious. In an early letter written on his way to Tibet, he says he feels as if he is being torn apart on the rack. “It pleases his divine majesty to draw my whole heart away with sweet and amorous violence to where the perdition of souls is great,” he wrote, “and at the same time with fastest bonds are my feet bound and drawn elsewhere.” He kept up that intense pitch in everything he did.

Desideri sailed from Rome to India in 1712. In 1714 he began walking from Delhi across the Himalayas to Lhasa—a trek that lasted 18 months. He slept on the ground, in the snow, and struggled with snow blindness and frostbite. At one point he made his way over a rushing river by clinging precariously to a bridge made of two vine ropes. To get through the Ladakh desert, he joined the caravan of a Tartar princess and argued about theology with her each night in her tent.

When he finally arrived in Lhasa, the king and the lamas welcomed him enthusiastically, and their enthusiasm didn’t wane when he announced that he was a lama himself and intended to convert them all to Catholicism. In that case, the king suggested, it would be a good idea for him to study Buddhism. If he really understood Buddhism and he could still convince the Tibetans that Catholicism was better, then of course they would convert.

Desideri accepted the challenge. He spent the next five years in the Buddhist monasteries tucked away in the mountains around Lhasa. The monasteries were among the largest academic institutions in the world at the time. Desideri embarked on their 12-year-long curriculum in theology and philosophy. He composed a series of Christian tracts in Tibetan verse, which he presented to the king. They were beautifully written on the scrolls used by the great Tibetan libraries, with elegant lettering and carved wooden cases.

But his project was rudely interrupted by war. An army from a nearby kingdom invaded, laid waste to Lhasa, murdered the king—and then was itself defeated by a Chinese army. Desideri retreated to an even more remote monastery. He worked on his Christian tracts and mastered the basic texts of Buddhism. He also translated the work of the great Buddhist philosopher Tsongkhapa into Italian.

In his book, Desideri describes Tibetan Buddhism in great and accurate detail, especially in one volume titled “Of the False and Peculiar Religion Observed in Tibet.” He explains emptiness, karma, reincarnation, and meditation, and he talks about the Buddhist denial of the self.

It’s hard to imagine how Desideri kept any sense at all of who he was. He spent all his time reading, writing, and thinking about another religion, in another language. (Thupten Jinpa, the current Dalai Lama’s translator, told me that Desideri’s Tibetan manuscripts are even more perceptive than the Italian ones, and are written in particularly beautiful Tibetan, too.) As I read his book, I could feel him fighting to retain his missionary convictions as he immersed himself in the practices of “the false and peculiar religion” and became deeply attached to its practitioners.

Desideri overcame Himalayan blizzards, mountain torrents, and war. But bureaucratic infighting got him in the end. Rival missionaries, the Capuchins, were struggling bitterly with the Jesuits over evangelical turf, and they claimed Tibet for themselves. Michelangelo Tamburini, the head of the Jesuits, ordered Desideri to return to Europe immediately, until the territory dispute was settled. The letter took two years to reach Tibet, but once it arrived, in 1721, Desideri had no choice. He had to leave.

Michelangelo Tamburini (Wikimedia)

He spent the next 11 years writing and rewriting his book and appealing desperately to the Vatican to let him return to Tibet. It had clearly become the only place where he really felt that he was himself. In 1732 the authorities finally ruled—in favor of the Capuchins. His book would not be published and he could never return. He died four months later.

Almost at the end of Desideri’s book, I came across a sentence that brought me up short. “I passed through La Flèche,” he wrote, “and on September the fourth arrived in the city of Le Mans.”

La Flèche? Where Hume had lived? I let out an astonished cry. The librarians, accustomed to Rare Book Room epiphanies, smiled instead of shushing me.

I headed to a café, wolfed down a sandwich (I was suddenly hungry again), and took stock of this new discovery. Could there be a connection after all?

The English Desideri was abridged. Could I find out more in the Italian book of missionary documents that Petech had described in his article? The seven volumes of the 1952 I Missionari Italiani nel Tibet e nel Nepal, never translated or reprinted, arrived from the storage facility the next day.

I called my brother Blake, an art historian who knows Italian (and French, German, Latin, and Anglo-Saxon), and got him to translate for me. Blake had been my mainstay through my darkest days, and I think he was immeasurably relieved that this time my late-night emergency phone call was about an obscure manuscript instead of a broken heart.

With Blake’s help, I made out a longer version of the passage about France. “On the 31st (August) around noon,” Desideri wrote, “I arrived at our Royal College at La Flèche. There I received the particular attention of the rector, the procurator, Père Tolu and several other of the reverend fathers. On the 4th I left La Flèche.”

So Desideri not only had been to La Flèche but had also talked with the Jesuits at the Royal College at some length. Reading Petech with Blake, I realized that the Jesuits at La Flèche might even have had a copy of Desideri’s manuscript. Petech described the history of Desideri’s manuscript in detail. He explained that Desideri had actually written multiple manuscripts about his travels. He wrote the first while he was sailing from India to France, and evidence suggests that he had this manuscript with him as he made his way from France to Rome in 1727. When he got back to Rome, he revised his text considerably, and six months later he produced a new manuscript. In this version, Desideri writes, “When I returned through France and Italy to Tuscany and Rome, I was strongly urged by many men of letters, by gentlemen and by important personages, to write down in proper order all I had told them at different times.” The reason? The religion of Tibet was “so entirely different from any other,” he wrote, that it “deserves to be known in order to be contested.”

So it was possible that Desideri had sent the Royal College at La Flèche a copy of this revised manuscript; the Jesuits regularly circulated such unpublished reports among themselves.

But Desideri visited in 1727. David Hume arrived at La Flèche eight years later, in 1735. Could anyone there have told Hume about Desideri? I couldn’t find any trace of Père Tolu, the Jesuit who had been especially interested in Desideri.

Maybe Hume’s letters contained a clue? I sat on my narrow sofa bed, listening to the rain fall, and made my way through his voluminous correspondence. To be immersed in Desideri’s world was fascinating but exhausting. To be immersed in Hume’s world was sheer pleasure. Hume writes better than any other great philosopher and, unlike many great philosophers, he is funny, humane, fair, and wise. He charmed the sophisticated Parisian ladies of the grand salons, though he was stout, awkward, and absentminded and spoke French with an execrable Scots accent. They called him “le bon David”—the good David.

Hume always described his time at La Flèche with great fondness. In the one letter of his that survives from his time there, he says he is engaged in constant study. La Flèche’s library was exceptional—reading books was a far better way to learn, he notes, than listening to professors. As for reaping all the advantages of both travel and study, he writes, “there is no place more proper than La Flèche … The People are extremely civil and sociable and besides the good company in the Town, there is a college of a hundred Jesuits.”

A later letter shows that Hume talked with at least one of those Jesuits at some length. He recalls walking in the cloister of the Royal College, his head “full of the topics of my Treatise,” with a Jesuit “of some parts and learning.” The Jesuit was describing a miracle, and this inspired Hume to come up with one of his cleverest skeptical arguments. A real miracle, he said, is by definition highly improbable, which means that deception or delusion is always a more likely—and therefore better—explanation. The Jesuit understood this reasoning (he was “very much gravelled,” Hume wrote) but said that it simply couldn’t be right, because if it were, you would have to reject not just the miracle in question but all the Gospels. “Which observation,” Hume the skeptic noted drily, “I thought it proper to treat as a sufficient answer.”

Who was this Jesuit “of some parts and learning?” Could he have been one of the fathers who had met Desideri eight years earlier? And whoever he was, what else did he and Hume talk about?

When you’re young, you want things: work, love, children. When you reach middle age, you want to want things. When you’re depressed, you no longer want anything. Desire, hope, the future itself—all seem to vanish, as they had for me. But now I at least wanted to know whether Hume could have heard about Desideri. It was a sign that my future might return.

I had thought I would spend that future alone; I was realistic about the prospects of a 50-year-old female professor. But then I had a romantic adventure or two.

They were adventures with both women and men. In my period of crisis I had discovered that I could have deep, sustaining friendships with women, as well as romance. I had been wrong about that part of my identity, too.

I was still fragile. A one-line e-mail from my ex-lover enveloped me in black depression once more. But the adventures were invigorating.

One of them happened in Montreal. I had grown up there, and went back to give a lecture at my old university. One evening I walked up St. Lawrence Boulevard in a swirling snowstorm toward a rendezvous. Suddenly, my 16-year-old self appeared, in a memory as vivid as a hallucination, striding through the snow in her hippie vintage fur coat, saying eagerly, as she often did, “I wonder what will happen next?”

Something was going to happen next, even if it wasn’t the new life I had longed for.

I got back to work. In 2007, I began the Moore Distinguished Visiting Fellowship at the California Institute of Technology, in Pasadena, glad to get away from my dark, cold room and melancholy memories. The school gave me a big sunny apartment looking out at the San Gabriel Mountains. I found myself able to write about children again, and I started my next book, The Philosophical Baby. But I kept working on the Hume project, too.

My philosophical detective story had driven me to find out more about the Royal College at La Flèche. If my atheism made me suspicious of the Buddhists, I was even more suspicious of the Jesuits. After all, at least in the traditional telling, the whole point of the Enlightenment had been to dispel the malign influence of the Catholic Church.

The Berkeley library had only one book about the college at La Flèche: Un Collège de Jésuites aux XVIIe et XVIIIe Siècles, 1,200 pages in four fat volumes with marbled covers, printed in 1889. I had waded through them before I left for Caltech, and had started to get a picture of the place. And then, fortuitously, my neighbor down the hall at Caltech turned out to be the historian of science Mordechai Feingold, one of the world’s leading experts on the 17th- and 18th-century Jesuits and their contributions to science.

For a long time, the conventional wisdom was that the Jesuits were retrograde enforcers of orthodoxy. But Feingold taught me that in the 17th century, the Jesuits were actually on the cutting edge of intellectual and scientific life. They were devoted to Catholic theology, of course, and the Catholic authorities strictly controlled which ideas were permitted and which were forbidden. But the Jesuit fathers at the Royal College knew a great deal about mathematics and science and contemporary philosophy—even heretical philosophy.

Hume had said that Descartes, Nicolas Malebranche, and Pierre Bayle inspired the Treatise. Descartes, I learned, graduated from the Royal College, and Malebranche’s most dedicated students had taught there, although the most-fervent Malebranchistes were eventually dismissed. Books by Descartes, Malebranche, and Bayle were in the college library—although they were on the Index, the Vatican’s list of forbidden books. (Hume’s Treatise would join them later.)

La Flèche was also startlingly global. In the 1700s, alumni and teachers from the Royal College could be found in Paraguay, Martinique, the Dominican Republic, and Canada, and they were ubiquitous in India and China. In fact, the sleepy little town in France was one of the very few places in Europe where there were scholars who knew about both contemporary philosophy and Asian religion.

The Jesuits documented everything, Feingold told me. If I wanted to know who had talked with Hume at La Flèche, I could go to Rome to find out.

Toward the end of my Caltech stay, I gave a talk at one of those TED-like conferences where successful people from different fields gather to inspire the young and impress one another. A large, striking, white-haired man in the audience nodded and laughed in an especially enthusiastic way during my talk. He turned out to be Alvy Ray Smith, a co-founder of Pixar.

Unlike me, Alvy had leapt into new lives many times. He had started out as a Southern Baptist boy in small-town New Mexico, and then had plunged into the wildest reaches of San Francisco’s counterculture. Later, he impulsively abandoned his job as a computer-science professor at NYU and took off again for California, because he felt “something good would happen.” Something did: Xerox PARC, where he helped invent the first color computer graphics, and then Lucasfilm, where he helped invent the first computer-generated movies. He leapt into entrepreneurship and created Pixar—and then left Pixar, to found a new company, which he sold to Microsoft. He retired on the proceeds. Now he lived in Seattle, where he collected art, proved mathematical theorems, and did historical research for fun.

His favorite motto came from Alan Kay, another computer pioneer: “The best way to predict the future is to invent it.” The conference went on for two days, and by the end of it, after a few long conversations but without so much as a kiss, he took another leap and decided that his next life would be with me. If I was a bit slow to realize it, that was okay. He was used to the fact that it took other people a while to catch up to his visions of the future, especially poky academics.

When my time at Caltech was up, I returned to my old beloved Berkeley house; my ex-husband had moved to Boston, and I had bought out his half. Alvy came to visit one weekend, and we began talking on the phone every night. I had decided to follow Feingold’s advice and go to the Jesuit archives in Rome, and I asked Alvy, rather tentatively, whether he would like to come along. It was an unusual venue for a date, but he found the prospect far more romantic than sitting in the sun by the Trevi Fountain. It seemed a good omen.

The archives are not easy to find—they are, appropriately, tucked away behind a corner of St. Peter’s Basilica. Finding the actual records was not so easy either. But on our very last day there, we discovered the entries in the Jesuit catalogs that listed everyone who lived at the Royal College in 1726, 1734, and 1737: some 100 teachers, students, and servants in all. Twelve Jesuit fathers had been at La Flèche when Desideri visited and were still there when Hume arrived. So Hume had lots of opportunities to learn about Desideri.

One name stood out: P. Charles François Dolu, a missionary in the Indies. This had to be the Père Tolu I had been looking for; the “Tolu” in Petech’s book was a transcription error. Dolu not only had been particularly interested in Desideri; he was also there for all of Hume’s stay. And he had spent time in the East. Could he be the missing link?

When I got back to California, I found nothing at all about Dolu in the Berkeley library catalogs. But Google Books had just been born, so I searched for Dolu Jesuit in all the world’s libraries. Alvy kept track of what we found, in an impressively thorough and complex spreadsheet.

We discovered that in the 1730s not one but two Europeans had experienced Buddhism firsthand, and both of them had been at the Royal College. Desideri was the first, and the second was Dolu. He had been part of another fascinating voyage to the East: the French embassy to Buddhist Siam.

In the 1680s, King Narai of Siam became interested in Christianity, and even more interested in European science, especially astronomy. Louis XIV dispatched two embassies to Siam, in 1685 and 1687, including a strong contingent of Jesuit scientists. Dolu was part of the 1687 group.

One of the other ambassadors was another extraordinary 17th-century figure: the abbé de Choisy. The abbé was an open and famous transvestite who gave the ladies of the French court fashion tips. He wrote a very popular and entertaining account of his trip to Siam. Hume had it in his library, along with de Choisy’s scandalous autobiography, The Memoirs of the Abbé de Choisy Who Dressed as a Woman. The abbé’s sexual fluidity was a good example of the adventurous, boundary-crossing spirit of the 17th century, which often leaves the 21st looking staid by comparison.

The Jesuits in the 1687 embassy, including Dolu, stayed in Siam for a year and spent a great deal of time with the talapoins—the European word for the Siamese Buddhist monks. Three of them even lived in the Buddhist monastery and followed its rules.

Like Desideri’s mission, the Siamese embassy ended in bloodshed and chaos. In 1688 the local courtiers and priests revolted against the liberal king and his arrogant foreign advisers. They assassinated King Narai, the new bridge between the two cultures crumbled, and the Jesuits fled for their lives. Several of them died. Dolu and a few others escaped to Pondicherry, in India, where they set up a Jesuit church.

In 1723, after his extraordinarily eventful and exotic career, Dolu retired to peaceful La Flèche for the rest of his long life. He was 80 when Hume arrived, the last surviving member of the embassies, and a relic of the great age of Jesuit science.

I had to piece together a picture of Dolu from contradictory fragments, mostly from his time in India. To Protestant English writers, he was a typical Catholic zealot. On the other hand, Catholic Capuchin writers, Desideri’s adversaries, attacked Dolu and his fellow Jesuits for their sympathy toward Hinduism. Dolu joined two other priests to break down the doors of a Hindu temple and destroy lamps and torches. But with Jean-Venance Bouchet, the head of the Indian mission, he also designed Catholic ceremonies that integrated Hindu traditions, and the Vatican disapproved. In fact, Bouchet became a noted scholar of Hinduism and adopted Hindu dress, ascetic practices, and even vegetarianism.

I also caught glimpses of Dolu the scientist. “There was never a more polite and generous man, nor one more learned about the natural world,” reported a periodical of the time. The Jesuits brought state-of-the-art 12-foot-long telescopes to Siam and then to Pondicherry, and they made important astronomical discoveries. I saw an engraving of King Narai of Siam gazing through one of the telescopes at a lunar eclipse.

Dolu had a sense of humor, too, and wrote satirical squibs and plays. An aristocratic intellectual named Saint-Fonds wrote to a friend that as an amusement, back in France, he had invited Dolu to lunch with Robert Challes, an intensely anti-Jesuit writer—indeed, an atheist—who had also traveled in Siam and India. Saint-Fonds hoped, he said, to enjoy the furious storm of controversy that would surely result. But instead, “I found myself in the midst of the gentlest breezes,” he wrote. “P. Dolu, the name of the missionary, under a wild beard, is a Jesuit per omnes casus, that is to say, polite and politic, and he understands witty repartee better than a man of the world.”

Dolu was an evangelical Catholic, and Hume was a skeptical Protestant, but they had a lot in common—endless curiosity, a love of science and conversation, and, most of all, a sense of humor. Dolu was intelligent, knowledgeable, gregarious, and witty, and certainly “of some parts and learning.” He was just the sort of man Hume would have liked.

And I discovered something else. Hume had said that Pierre Bayle’s Historical and Critical Dictionary was an important influence on the Treatise—particularly the entry on Spinoza. So I looked up that entry in the dictionary, which is a brilliant, encyclopedic, 6 million–word mess of footnotes, footnotes to footnotes, references, and cross-references. One of the footnotes in the Spinoza entry was about “oriental philosophers” who, like Spinoza, denied the existence of God and argued for “emptiness.” And it cross-referenced another entry about the monks of Siam, as described by the Jesuit ambassadors. Hume must have been reading about Buddhism, and Dolu’s journey, in the very building where Dolu lived.

What had I learned?

I’d learned that Hume could indeed have known about Buddhist philosophy. In fact, he had written the Treatise in one of the few places in Europe where that knowledge was available. Dolu himself had had firsthand experience of Siamese Buddhism, and had talked at some length with Desideri, who knew about Tibetan Buddhism. It’s even possible that the Jesuits at the Royal College had a copy of Desideri’s manuscript.

Of course, it’s impossible to know for sure what Hume learned at the Royal College, or whether any of it influenced the Treatise. Philosophers like Descartes, Malebranche, and Bayle had already put Hume on the skeptical path. But simply hearing about the Buddhist argument against the self could have nudged him further in that direction. Buddhist ideas might have percolated in his mind and influenced his thoughts, even if he didn’t track their source. After all, contemporary philosophers have been known to borrow ideas without remembering exactly where they came from.

I published an article about Hume, Buddhism, and the Jesuits, long on footnotes and short on romance, in an academic journal. As I was doing my research, many unfailingly helpful historians told me that my quirky personal project reflected a much broader trend. Historians have begun to think about the Enlightenment in a newly global way. Those creaky wooden ships carried ideas across the boundaries of continents, languages, and religions just as the Internet does now (although they were a lot slower and perhaps even more perilous). As part of this new global intellectual history, new bibliographies and biographies and translations of Desideri have started to appear, and new links between Eastern and Western philosophy keep emerging.

It’s easy to think of the Enlightenment as the exclusive invention of a few iconoclastic European philosophers. But in a broader sense, the spirit of the Enlightenment, the spirit that both Hume and the Buddha articulated, pervades the story I’ve been telling. The drive to convert and conquer the “false and peculiar” in the name of some metaphysical absolute was certainly there, in the West and in the East. It still is. But the characters in this story were even more strongly driven by the simple desire to know, and the simple thirst for experience. They wanted to know what had happened before and what would happen next, what was on the other shore of the ocean, the other side of the mountain, the other face of the religious or philosophical—or even sexual—divide.

This story may help explain Hume’s ideas. It unquestionably exemplifies them. All of the characters started out with clear, and clashing, identities—the passionate Italian missionary and the urbane French priest, the Tibetan king and lamas, the Siamese king and monks, the skeptical young Scot.

But I learned that they were all much more complicated, unpredictable, and fluid than they appeared at first, even to themselves. Both Hume and the Buddha would have nodded sagely at that thought. Although Dolu and Desideri went to Siam and Tibet to bring the wisdom of Europe to the Buddhists, they also brought back the wisdom of the Buddhists to Europe. Siam and Tibet changed them more than they changed Siam and Tibet. And his two years at La Flèche undoubtedly changed David Hume.

Hume and the Jesuits and Siam and Tibet changed me as well. I’d always thought Hume was right about the self. But now, for the first time, I felt that he was right.

In 2010, Alvy and I got married—the future reinvented. Once again, I was an exceptionally fortunate and happy woman, full of irrational exuberance and everyday joy. But that’s not all I was. I’d discovered that I could love women as well as men, history as well as science, and that I could make my way through sadness and solitude, not just happiness. Like Dolu and Desideri, the gender-bending abbé and the Siamese astronomer-king, and, most of all, like Hume himself, I had found my salvation in the sheer endless curiosity of the human mind—and the sheer endless variety of human experience.