FORTUNE -- What is it exactly that makes some people command far more respect and attention, even devotion, than their peers? And if you're not born with the kind of magnetism that compels people to admire and follow you, can you acquire it? "Charisma" comes from a Greek word that means "gift from the gods," which may explain why most of us assume you've either got it or you don't.
John Neffinger and Matthew Kohut beg to differ. Co-founders of KNP Communications, a coaching firm with a client roster of high-powered executives, politicians, and media stars, the pair set out a few years ago to break charisma down to its component parts. "We studied the most compelling people to see how they pulled it off," they write. "From Oprah Winfrey to Ronald Reagan, from Dolly Parton to the Dalai Lama, we saw successful people using the same strategies over and over."
Those strategies are spelled out in Compelling People: The Hidden Qualities That Make Us Influential. The book, which includes some material the authors have already taught as lecturers at a few top B-schools, is now required reading at Harvard, Columbia, and the McDonough School of Business at Georgetown.
It turns out that the ineffable thing we call charisma has two primary elements, strength and warmth. Strength, by the authors' lights, is "a person's capacity to make things happen," while warmth is "the sense that a person shares our feelings, interests, and view of the world." Getting elected to public office usually takes both. For instance, the authors note, "George W. Bush ran in 2000 as a compassionate (warm) conservative (strong)."
Sounds good, but there's a catch: Balancing the two qualities, which are fundamentally different or even opposed, is tricky. Warmth -- including friendliness, openness, and a disarmingly self-deprecating sense of humor -- may make you likeable, but it doesn't necessarily command respect, while strength alone can come across as icy or even scary. What we call charisma, magnetism, or executive presence is the knack of projecting both at once -- an ability, the authors observe, that is "so rare that we celebrate, elevate, and envy those who manage it."
Not to worry. Compelling People goes into exhaustive detail about how to be -- or seem -- strong and warm at the same time, addressing everything from how and when to smile, to how to modulate your voice in given kinds of situations, to the specific eyelid-tensing technique behind Clint Eastwood's famous power stare.
If you've never given much thought to basics like simply shaking hands, the book suggests you start. The key, apparently, is applying "conscious focus" to preparing the flexors and extensors in your fingers: "It is important that your handshake match that of the person you are greeting," whether it's bone-crushing or dead-fish, so "keep those hand muscles flexed as you go in, and you'll be ready for any grip strength you come across."
Naturally for a couple of communications coaches, the authors offer remedies for habits of speech that undermine people's influence at work. One of these is "uptalk," that annoying Valley-girl intonation that makes every sentence turn up at the end like a question. It's a verbal tic that inadvertently signals "submissive approval seeking" and "creates the impression the speaker is uncertain about things that should not be in doubt" -- neither of which conveys strength (or warmth either, for that matter). Unfortunately, uptalk can be a tough habit to break. If you suspect it's holding you back, the authors recommend recording yourself and "forcing yourself to endure listening" to how uninspiring you sound.
Although Compelling People aims to show you how to be your own charisma coach, the authors are careful to avoid leaving the impression that, once you've mastered all of their tricks, you're done. Cultivating one's own personal magnetism is a process that never ends, it seems.
"Ronald Reagan had decades of professional acting experience before he brought his grandfatherly cowboy persona to the national stage," the book points out. "Even after years as a successful politician, Bill Clinton sought out every expert he could find to learn how to connect with people better. The best communicators are the ones who realize how much room they still have for improvement."
Even President Obama, generally considered to score pretty high on charisma, could tweak a few of his mannerisms, according to the authors -- for example, a habit of speaking with his chin raised so that he is literally looking down his nose at his audience: "[Obama] has been guilty of wearing this expression on many occasions and, when he does, his demeanor goes from cool to cold." The takeaway: Unless you happen to already hold the most powerful job in the free world, try to keep your chin level while you're talking.
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