Certain jobs somehow lend themselves towards informal conversation. There's the hairdresser who blow-dries while discussing who's sleeping with whom, the bartender who consoles the heartbroken with a pint of Sammie, the J. Crew saleswoman who becomes your body-image consultants. Then, of course, there is the cabbie.

You look at him sitting in the front seat, wearing a scruffy, dark sweater, glancing in the rearview mirror. As you give directions and he begins to weave through traffic, a conversation soon evolves. You talk politics, discuss the weather, or tell him a bit about your classwork. The exchange is natural and familiar. Pavlov would have had a field day with this one.

There is something about these men that makes them worth talking to. They hold more conversations with complete strangers in one week than many of us will in a lifetime. Indeed, they are true men of the people, certain sultans of small talk.

Meet Carlos Hernandez, a Cambridge cab driver for the Yellow Cab Company. He has curly black hair, dark skin and a slightly rotund physique. He is soft-spoken yet intelligent, and eases into casual conversation with the fluidity of a professional. "I give rides to the whole spectrum of society, from the lowest to the highest," he says with a charming Spanish accent. "I pick up professors, I pick up students, I pick up drug dealers, I pick up pimps.... I'm very open-minded when I talk to people."

Carlos has served a twelve-year stint with the Yellow Cab Co., working nights. He claims no divine source of inspiration in choosing the job. After emigrating from El Salvador 20 years back, he found himself in need of work. Getting his taxi license, known in cab jargon as a "hacking license," was the obvious choice. "No matter how bad the economy is," he says, "you can always get a job as a cab driver." It is steady work, which he enjoys mostly because of the variety of people he meets.

With veteran status, Carlos considers himself a sage of the streets. He has picked up some wisdom along the way as well as countless intriguing stories. Over the years, he claims to have accepted fares from Harvard notables: Neil Rudenstine, Alan Dershowitz, Henry Louis "Skip" Gates and Stephen Jay Gould, and real-world gurus like George Will, a columnist for Newsweek. Carlos describes Rudenstine as "very humble, very down to earth," and Gates as "a real nice, fun guy, a Democrat." He recalls driving Gould to Logan airport, and having "a great conversation about creation versus evolution science."

Though Carlos has the gift of gab, he admits that conversations with his customers rarely reach a personal level. However, occasionally, especially late on weekend nights as the bars empty, people decide to bare their souls. "They've had a few drinks and they might be having some problems, you know?" he says. "They have something that's bugging them and they think, I'll never see this guy for the rest of my life."

Or so they think. Carlos recalls recently picking up a man who had given him an intimate account of his personal problems during a separate ride a couple months ago. "I picked him up, he recognized me, and he said, 'Oh my God! I don't believe it!'.... It's a very small world, you know?"

Working nights, Carlos says that he sees lots of strange things, especially with the college crowd. Every weekend, he finds himself taking countless inebriated Harvard students back to the Square. "They like to party," he points out. He must have had a few drinks himself.

Of course, some students go too far in their quest for a good time, and Carlos finds himself in an awkward position. "They like to make out with their girlfriends," he says. "I'm a guy, and I get a little uncomfortable.... I look over here, and they're already lying down on the seat.... They get to a certain point, and I start to think, that belongs in the bathroom, not in my car."

Sometimes, students' recreational activities border on plain vulgarity. On extremely rare occasions, Carlos is forced to take disciplinary action. "One time I kicked out four Harvard students (from my cab). They were being rude, farting inside the car and laughing. I told them I didn't want any part of that. I stopped the cab and told them to get out."

In addition, Carlos recalls being offered money "for sex" more that once. He clarifies that the money is not a proposition but a request to restrain his sometimes wandering eyes from the rearview mirror. "They tell me, 'Just drive around.' But I say, 'No way.'" Carlos assumes there are other cab drivers who don't care about sex in the backseat, and take the money.

Some passengers also use offensive language in his cab, which Carlos does not approve of. "You know how they say a guy 'talks like a sailor.' Now the girls, too. I jump sometimes when I hear this kind of talk." Recently, Carlos recalls driving two female students from a bar late at night. One of the women, he says, was "very upset," and had "had a few drinks." She used indecent language in reference to the unimpressive size of her boyfriend's genitalia. "She's looking at me in the rearview mirror, and I'm thinking, 'What the heck? Who is this girl?'"

Despite such outlandish occurrences, Carlos says that Harvard Square is a pretty calm place, especially in comparison to other areas in the city. Carlos has never been robbed, nor had a gun pulled on him. Nevertheless, he acknowledges that driving a cab can be dangerous, and that other drivers have had very frightening experiences. "A friend of mine was shot in the arm for no reason," he says.

Driving around the city every night until dawn, Carlos encounters some of Cambridge's most well-off, elite citizens. But appearances don't tell the full story. He once picked up "a young professional woman near the Business School. She wanted to go downtown to buy crack. She was having her relatives over the next day. She said she was all tense and needed that release. She says she does it all the time".

Interestingly, Carlos says that the size of the tips he receives has little to do with a passenger's wealth. In fact, he adds, "People who live in the better neighborhoods are the tightest.... The average, hard-working, middle class guys are the most generous."

Carlos is somewhat ambivalent regarding the tipping practices of Harvard students. "Harvard students are okay," he says. For the most part, he points out, "they're not wealthy." But at least Harvard students haven't jumped out of his cab without paying up like the kids at Bentley College and Pinehill, amongst others. "College students are crazy, you know? It doesn't happen that much but for a cab driver it's too often. That's money out of my pocket. They say 'oh, right here.' As soon as you pull over, they just take off."

Carlos says that the Harvard students he drives are almost always friendly and polite. His one criticism refers to a familiar, time-honored tradition of Harvard conversation: the interminable whine. "They're always complaining that (their classes) are too hard," he says with laugh. "I understand that they've got a lot of work."

Carlos has been asked to put the pedal to the metal more times than he can remember. When trying to get to Logan in under 15 minutes, Carlos tells his passengers: "No, get a helicopter".