One week last spring, before Apple started promoting the lectures on its home page, one of Dreyfus' philosophy and literature lectures -- he calls it "From Gods to God and Back" -- ranked 58th among podcasts on iTunes. It trailed programs from the BBC and Comedy Central but was downloaded more often than NPR's "This I Believe" and NBC's "Meet the Press."
To improve the sound quality of his lectures, Dreyfus agreed to teach in a room outfitted with a microphone and special recording device. But he is ambivalent about the benefits of broadcasting his philosophy class to the world. He said 25% of his enrolled students cut class.
One of the occasionally absent is Alexander Diaz, 18, a second-year philosophy major from Downey. He says he skips roughly every third class and listens, with his feet up, to the missed lectures through his iPod headphones on his back porch while he takes notes in the margins of Heidegger's "Being and Time."
"I'm pretty honored to take the class, but at the same time, when he does his lectures, it's not like I'm there with Dreyfus the man," Diaz said, referring to the impersonal feeling of sitting in a large lecture hall.
Dreyfus, who has taught at Berkeley since 1968, has long questioned the effectiveness of distance learning. In his 2001 book of essays, "On the Internet," he called the practice a "disembodied telepresence" and worried that remote students would take fewer risks than those sitting face-to-face with their instructors.
But Dreyfus says the chance to disseminate ideas softens his reservations. And the e-mails he receives from the listening audience -- "you podcast people," he calls them during class -- are touching.
Zachary Streitz soaks up the philosophy lectures as he baits hooks on a 58-foot fishing boat in the Gulf of Alaska, where he trawls for halibut and black cod. On shore, the 30-year-old fisherman loads up on course books.
"There are enough hours spent here that my hands are involved in the repetition that is my work, and my mind has more or less free rein to wander," he wrote to Dreyfus in June 2006. "If ever you are in need of any halibut, let me know."
Joe and Diane Mercier, who live outside Weaverville in Northern California's Trinity County, get their Dreyfus fix over morning coffee. They also listen to Muller's physics class from UC Berkeley and a Stanford course on geography and world cultures.
Joe, a 60-year-old evidence officer for the county Sheriff's Department, is annoyed by some of the routine instructions that begin and end classes as well as the sound of a student's phone ringing or a professor scolding someone for leaving early.
But he and his wife revel in the moment when Dreyfus dispenses with administrative work with his usual, "OK, here we go" and plunges into a philosophical discussion.
"We listen to relieve ourselves of mainstream television," Joe said.
He occasionally writes the papers that Dreyfus assigns but hasn't submitted any, unsure whether they would be read.
Arthur Marquis, 59, a former Justice Department attorney in Long Beach, told guests at his retirement party last year that he wanted to use his newly free time to see the world differently. They laughed.
Marquis, who graduated from UC Berkeley's law school decades ago, started taking French lessons at a local school. He found Dreyfus on iTunes and then bought an iPod so he could listen on his treadmill or outdoors.
"It's like electronic schizophrenia," he said. "I can hear voices in my head, and it's Dreyfus."
While other truck drivers talk to one another on their CB radios, Wood prefers to pass time on his weeks-long routes by sampling from an academic smorgasbord. He has listened to classes on astronomy from Ohio State University, geography from UC Berkeley and behavioral endocrinology from Johns Hopkins in Baltimore, which makes podcasts available through its website but not iTunes U.
"I'm a curious person," said Wood, who comes from a family of Pentecostal ministers and missionaries.
He attended the University of Alaska in the 1960s and remembered only one thing from his philosophy class: the name Kant (which belonged to the 18th century German thinker Immanuel Kant). He worked as a wood and stone turner until the dust started bothering him. In 2002, he became a truck driver.
This spring, he found the lectures on iTunes. "I felt like I discovered the Fountain of Youth," he said.
Wood doesn't listen to classes during his one week off the road each month, only when he's behind the wheel.
"For me, driving and listening are bound together like space and time," he said.
Sometimes, the classes that involve math or obscure concepts such as string theory lose him. But not Dreyfus' class, which he finds electrifying.
He remembers being somewhere in western Kansas in April when he heard Dreyfus' concluding lecture on existentialism, during which the professor asked students to vote, by raising their hands, for their favorite philosophies.
Dreyfus offered a thumbnail description of each: traditional Christianity, with God the creator and heaven; Kierkegaard's unconditional commitment to another person or cause; Dostoevski's unconditional commitment to all human beings; Nietzsche's belief in different identities, a life more like a series of short stories than a novel.
Wood, who long ago broke away from his family's religion, voted for Nietzsche silently.
"OK, that's it," Dreyfus said. "I have to stop and hand out the evaluations."
The class erupted in a sustained ovation, whooping and whistling.
The course had been recorded a year earlier. But Wood, separated by space and time, clapped and whooped too.
"Big trucks have enormous inertia. They practically drive themselves," he said. The machine, indifferent to his emotions, powered on, his body molded to the wheel, his mind having a great ride.