Like Greek philosophers and Brazilian soccer players, we routinely go by single names nowadays. Just as asking for someone's first name in years past seemed presumptuous, so does inquiring about their last name today. ("Don't get personal!") When a waiter introduces himself by saying "I'm Jason. I'll be your server tonight," responding, "What's your last name, Jason?" would be a serious breach of protocol.

In the first-name society, asking to be addressed by your surname sounds stuffy and old-fashioned. Sticking to given names suggests breezy informality; the verbal equivalent of wearing shorts to restaurants. But other factors are involved here, ones that have little to do with informality.

"First-naming" someone you don't know is an effective way to get the upper hand. One way Southern blacks were kept in their place was by being called only by given names. The reason police officers say little to drivers they've pulled over before examining their license is so they can address them by their first name. ("Do you realize how fast you were going, Edna?")

"It's cop psychology to use first names when talking to a suspect," says a policeman in Lawrence Sanders's "The Second Deadly Sin." "It diminishes them, robs them of dignity. Like stripping a man naked before you question him."

Addressing those we've just met by surname and honorific is a sign of respect. ("Good to meet you, Mr. Jones.") Asking permission to address them by given name is an act of courtesy. So is granting that permission. This is why so many who grew up in a more mannerly time find it jarring to be first-named by someone who doesn't know them. They sense intuitively the disrespect involved.

A business consultant who asked readers of an Ohio newspaper how they felt about being addressed by their given names was inundated with responses. Most didn't like the practice. Older readers were particularly annoyed about being first-named by younger nurses, waiters, bank tellers, service personnel, and sales clerks. One 81-year-old woman left her dentist because his young hygienist wouldn't use her surname. Another woman asked a salesman where he'd learned to address customers by their first name. "In business school," the salesman responded.

Blame Dale Carnegie. America's original self-helper touted the "subtle flattery" of addressing new acquaintances by name. Carnegie suggested we follow the lead of James Farley, Franklin Roosevelt's postmaster general, who claimed to be on a first-name basis with 50,000 Americans. Millions of Carnegie readers and course graduates followed Farley's lead.

"Swingers" – who shared sex but not surnames – were another harbinger of the first-name society. So were Summer-of-Lovers who routinely exchanged only given names or nicknames. "A good hippie had no last name," observed commune veteran Mark Vonnegut (Kurt's son). The same thing is true of support-group members, especially ones in Twelve-Step gatherings that forbid use of surnames. The more popular such groups have grown, the more comfortable it has become to address strangers by their first names. Doing so feels casual, cordial, even intimate.

It is nothing of the kind. Far from being intimate, sharing first names alone is impersonal. Dispensing with surnames reflects wariness more than informality. In a guarded time like ours, revealing two names to another person ratchets up one's level of exposure. Once someone knows both of your names, that person can guess your ethnicity, your ancestry, your country of origin. He or she might be able to figure out who your parents are, and could have heard that your cousin Mike is in jail. And, of course, those who possess your surname can Google you on the Internet.

In the ID free-for-all of cyberspace, chatters seldom share one genuine name, let alone two. Cybercommunities are like an electronic Mardi Gras, a setting in which few participants are who they seem to be, and everyone can cut loose.

Central to this freedom is the careful guarding of one's surname. During years spent covering technology for The New York Times, reporter Michel Marriott found that using his actual name in chat rooms was a real conversation stopper. Doing so made Mr. Marriott feel like a nudist at a costume party.

On and off the Net, not giving up our surname allows us to substitute candor for intimacy. Like strangers on a train, those who don't identify themselves fully are free to share secrets because they know their relationship has no traction. No matter how friendly it may appear to first-name those we don't know well, doing so seldom leads to actual friendship.

The promiscuous use of given names is too faux familiar. What it really reflects is fear of genuine engagement. By becoming a first-name society we've exchanged the actual familiarity of two names for the feigned familiarity of one.

• Ralph Keyes is the author of "The Post-Truth Era" and, most recently, "The Quote Verifier."