Americans today are "no closer to a satisfactory theory of It," Roach believes, but they "have recourse to a well-stocked slang lexicon, including stuff, spunk, and moxie."

Ever since Weber's work in the 1920s, sociologists in the West have usually treated charisma in a circular fashion: We know who has it by looking at who's popular. Studies have focused mainly on politicians and businessmen, with some scholars arguing, especially in the 1980s, that we know charismatic leaders because of their "transformational" style of leadership - they are the CEOs who don't just steady a ship, but help it change course. What's most striking about charisma studies, however, is how few there are. "Generally speaking," writes Jennifer Merolla of Claremont Graduate University, with two coauthors, "political scientists have been hesitant to pursue, and a few have even argued against, the study of charisma." It's just seen as too elusive to waste one's time on.

But lately some researchers have been more ambitious, trying to break charisma into its components. Ronald Riggio, of Claremont McKenna College in California, argues that charisma is essentially a species of communication; in his research, he breaks charisma into parts like "expressivity," "control," and "eloquence." And Riggio found that presidents considered charismatic, like Reagan and Lincoln, used far more metaphors in their speaking than the noncharismatic.

Others talk about how extraneous information can influence audiences. In 2005, magician Steven Cohen, author of "Win the Crowd: Unlock the Secrets of Influence, Charisma, and Showmanship," told Psychology Today magazine that he began handing out a biographical card to audience members before a show; the card mentioned that Cohen had entertained numerous corporate executives and TV personalities. "The audience's reaction to me was immensely better," Cohen said. "They think, 'I better pay attention to him because these people have.' "

One student of charisma thinks that Oprah Winfrey may be the most charismatic American of us all. John Neffinger is a founder of KNP Communications, a consulting firm that teaches clients how to be more charismatic through a particular combination of traits: strength plus warmth. "Winfrey shows lots of warmth both towards suffering people in her stories and towards people in her audience (i.e., 'You get a car!'), and her nonverbals show she genuinely shares their sorrows and joys," Neffinger says. "But she is also very stern and tough on folks who she feels have done wrong (just ask James Frey)."

Drawing on the work of Harvard and Princeton psychologists as well as the American National Election Studies, KNP emphasizes "nonverbal cues," the aspects of how a person's physical carriage combines with his words to himself to be persuasive. Nobody is better at this, Neffinger argues, than Winfrey, but other examples of strength mixed perfectly with warmth include Ann Richards and Fred Thompson. And, of course, "Reagan and Clinton are the two obvious examples." Not to mention Barack Obama, "24" actor and insurance pitchman Dennis Haysbert, and English actor Idris Elba.

"Strength is conveyed primarily with posture and gestures," Neffinger says. Good, erect posture is strong. Holding one's hands palms up and facing away is weak, as are "self-comforting" gestures, like rubbing one's arm. Warmth is conveyed mostly by a genuine smile (in which the eye muscles smile in addition to the mouth muscles); but one must not smile in a way that undermines strength.

"Raising your eyebrows can signal surrender, and angling them the wrong way can give you puppy-dog eyes," Neffinger says. "That might get you out of some trouble, but it won't get you elected."

Neffinger's theory of charisma - strength plus warmth - can of course be seen as another version of Roach's argument about charisma's being rooted in conveying contradictions. This similarity became even clearer when I asked Neffinger about people who are charismatic in ways other than speaking. "Musicians who lead with both their tough and sensitive sides count, too," he said. "Elvis was a tough greaser who crooned love ballads to his sweetheart - that'll do it."

It might be added that Elvis was also a white man making black-influenced music; there's that racial doubleness again, which in another version so many black Americans share. To people who don't participate in what W. E. B. Du Bois called double consciousness - "an American, a Negro; two warring ideals in one dark body," Du Bois wrote - the ability of black or partly black Americans to move between cultures can be a source of amazement, and envy. Except perhaps for Bill Clinton, there is no white personality who can speak familiarly to both whites and blacks as skillfully as Tyra Banks or Oprah Winfrey can. In a multiracial society, blacks are the "omni-Americans," in the words of literary critic Albert Murray. Once slave, now free - they embody the contradictions at the heart of America itself. That doesn't make every black person charismatic, but it helps.

It would seem, then, that there is the charisma we're born with and the charisma we cultivate. I can't develop a biography like Diana's any more than I can become African-American. And Roach, for his part, is skeptical that people can learn to be charismatic. But Neffinger argues that the particular combination of strength plus warmth is appealing in any speaker; even if the highest level of charisma may be unobtainable for most of us, an enhanced level of charisma is, by learning certain nonverbal cues (and, Neffinger would add, marrying them to well-written speeches), within grasp.

"Think of it this way," Neffinger says. "There is no special charisma pheromone or incantation. The effect is all produced by very ordinary behaviors - moving around, speaking. The trick is these ordinary behaviors are performed in specific, extraordinary sequences that taken together leave the unmistakable impression of charisma."