He disliked overhead lights, in which category he included the midday sun, but he loved the horizontal rays at the two ends of the day. He waited for hours, reading a book, for the right sort of light and the right sort of weather.

When he came home, he developed his photographs and sorted them. Of a thousand pictures, he might keep three. When he decided that a picture was worth saving, he took it to a professional processor in London and had the processor hand-paint out all aspects of the image that he found distasteful, which meant all evidence of the twentieth century—cars, telegraph wires, signposts—and usually all people. Then he had the colors repeatedly adjusted, although this was enormously expensive, until they were exactly what he wanted—which was a matter of fidelity not to the scene as it was but to an idea in his head.

Other than his trips to Venice and St. Petersburg, the only reason he left All Souls for any length of time was to travel to America, to teach. He had appointments at Harvard, Rutgers, and N.Y.U.: he wanted students, because he found that it was discouragingly difficult to persuade older philosophers to change their minds. He also needed students, because only they would talk philosophy with him for twelve hours at a stretch and then wake up the next day wanting to do it again. Older philosophers (and his students from past years were now in this category) had children and spouses; they sat on academic committees and barbecued in their back yards. Only he stayed the same—as fervently single-minded as they were, too, when they were young. When he found a bright new student to mentor, he devoted hours to reading his work and writing comments. (He did this for many colleagues as well: he read with astonishing speed, and would often return a manuscript with densely argued comments that were longer than the manuscript itself, even if the manuscript was a book.)

When he was in America, he was compelled to procure his own food. Because he didn’t want to waste time on choice or preparation, he developed rigid routines that he could follow without thinking. For years, according to a colleague, he made the same meal every morning for breakfast, which he conceived of as a recipe for maximum health: sausage links, green peppers, yogurt, and a banana, all in one bowl. One day, the colleague’s nutritionist wife explained to him that this was not a particularly healthy meal, and suggested a better meal; the next day he switched to the new meal and never varied it.

He was always conscious of how little time he had. When he had to go from one building to another on a big American campus, he ran. But his routines were not just about time-saving: he found himself constantly returning to the same thoughts, philosophical and otherwise—that was just the way his mind worked. “At one point, I spent a year at Harvard when he was visiting there and we would go out to dinner,” Larry Temkin, a philosopher and former student of his, says. “We went to the same place, a Thai restaurant, every time, and every time he would order some curry and I would order something that had pineapples and rice and cashews. And every time he’d say, ‘Larry, isn’t that boring, don’t you want some of my curry?’ I’d say, ‘No, Derek, I don’t like curry, it’s too spicy for me.’ And then the next week we’d go to the same restaurant, and he would order the same meal, and I would order the same meal, and he’d say, ‘Larry, isn’t that boring, don’t you want some of this?’ And I’d say, ‘No, Derek, I really don’t, you like the curries, but they’re too spicy for me.’ And the next week the same thing would happen again. It was like ‘Groundhog Day.’ ”

Theo Parfit married an American, settled outside Washington, D.C., and had three children. She studied social work and became an expert on families. She wrote about how to hold families together in a crisis, and about ways to involve families in the education of their children. Although she lived far away, she kept in touch with her parents and siblings and cousins. She tried to see her brother when he came to the East Coast, as he frequently did, to teach, but usually he didn’t call. He didn’t do this to avoid her—it simply didn’t occur to him, because he was thinking about philosophy. She knew this, and tried not to feel hurt. When they did see each other, he was very friendly.

Parfit lived near his parents in Oxford, and saw them once a week, for Sunday lunch. His mother read up on philosophy to try to understand his work, but since Parfit saw her only with his father they couldn’t talk much about it. His father was baffled by him; he couldn’t understand why he became a philosopher—he thought he ought to have been a scientist. He tried, unsuccessfully, to interest his son in tennis.

Joanna struggled to find work. Finally, she managed to qualify as a nanny. She became pregnant and had a son, Tom, whom she raised on her own. A few years later, she adopted a daughter. She loved her children, but they didn’t make her happy. Every few months, she telephoned Parfit to talk to him about how depressed she was and how badly things were going. He dreaded those calls. Then, in her thirties, she died in a car crash.