BARBARA COOK walked onstage recently at the Peter Jay Sharp Theater at Juilliard carrying what appeared to be a massive, mutant tangerine with handles. On closer inspection, it was revealed to be merely an oversize purse of a peculiarly vivid hue, but it still looked incongruous against her clean black ensemble. She plopped it down beside a chair, where it sat for the two-hour duration of the master class she conducted for aspiring singers.

That bag's eye-catching oddity could be seen as emblematic of the central lesson this peerless artist struggled to impart to six students from the school's classical program. Love me, love my funky orange purse, she seemed to be saying. This is who I am, and, guess what? It matters to my art. Everything about me does. With a stern insistence belied by the radiant warmth she exudes with every chuckle and every sigh, Ms. Cook repeatedly urged her students to "put your life into what you do." If you're an orange-purse lover, use it!

This appeared to be a radical, possibly life-altering message for the six budding performers who bravely took the stage in front of a public audience to be put through the paces of learning how to sing musical-theater songs the way Barbara Cook likes them to be sung: truthfully, borne aloft on the natural rhythms of human speech, and passionately, as if the world hinged on a whispered confession of love or a man that got away.

It's the way Ms. Cook has been singing them for about half a century, as her many admirers well know, and it is what makes her the most accomplished, most vital exemplar of a tradition that is in danger of going the way of the dodo. If the honesty and purity Ms. Cook brings to the art of singing theater songs can be instilled in vocalists trained in a different tradition - as these gifted but still unformed students clearly had been - so much the better for lovers of classical music.

Ms. Cook, who gives several master classes a year around the country, opened the session with a brief, informal speech emphasizing that the key to good singing is making a real investment of feeling in each note. "Your own humanity," she said, "is your pathway to artistry."

Using a vivid metaphor that acknowledged the scariness of the enterprise, she explained, "We have to find the courage to take off our emotional clothes." Ms. Cook elaborated on that danger in speaking of the essential fear that crawls around in most performers' hearts, an anxiety that in a curious way may also be a motivating factor in the desire to become a performer: "We feel that we're not enough, that the world doesn't want us."

Plain but potent words, and not just applicable to performers. The therapeutic industry thrives on them, after all, as do innumerable Internet dating services. In fact, as Ms. Cook delightfully implied, referring to "this icky kind of talk" that prefaced the class proper, if you'd wandered in off 65th Street you might have concluded that Ms. Cook was conducting a self-help seminar, not a class in musicianship.

Magically, this two hours of unstructured instruction turned out to be a little of both. It was all the more rewarding for its dual purposes, for the students certainly, but also for an audience that included several accomplished performers ( Maria Friedman and Michael Ball of "The Woman in White," and Melissa Errico), who watched with rapt attention as Ms. Cook slowly coaxed out from behind the chilly armor of their presentational personae the radiant human beings lurking quietly within.

The first singer, a burly young tenor named Alex Mansoori, was welcomed to the stage and allowed to sing a selection straight through to the finish. That wouldn't happen often, and in fact as soon as he had finished Ms. Cook made clear that Mr. Mansoori's performance - of the song "The Cuddles Mary Gave," by Lynn Ahrens and Stephen Flaherty - wasn't much to her liking, despite the pearly purity of his tone.

She heard too much singing, not enough being. Coaxing him to stay away from the "stilted speech" she wryly noted aspiring opera singers are trained to employ, Ms. Cook had him simply speak the words of the song, a device she would use again and again. What poured out were similar streams of pretty, perfectly pitched sounds that didn't bear much resemblance to the "Amurrican" English she jokingly called for, or come close to communicating the meanings of their songs.

The students were hiding inside the music, inside their technique, and Ms. Cook set about dragging them out and making them lay bare their own truths, even if it meant awkwardness, embarrassment and some blunt criticism - leavened, in all cases, by sincerely delivered hugs and kisses. She put forth a telling paradox: "The place that seems most dangerous is exactly where safety lies." In other words, self-exposure and the abandonment of technical propriety, scary as it was, was the surest, the best, maybe the only way to communicate with an audience.

The truth of this insight was illustrated before our eyes, and it was a fascinating process to watch. Erin Morley, a soprano with a bright, silvery tone, sang "With You," a flowery ballad from "Pippin." "I don't hear you letting us in," Ms. Cook said, and tried to strip away all the mannerisms Ms. Morley had been trained to use in recital.

When she started in on the song again, Ms. Cook stopped her virtually before she started: "I can still see her gathering herself to sing," Ms. Cook said, to the audience, and once again implored Ms. Morley to let her real self into the song, and invite the audience with her. "You don't need to do that," she said, referring to the performing stance Ms. Morley kept donning like a costume. She reiterated her encouraging mantra: "You are enough."

The breakthrough came for Ms. Morley when Ms. Cook called Mr. Mansoori back to the stage, made them sit down knee to knee and hold hands, and then asked Ms. Morley to speak the words to him, adding music only when, after a few bouts of enforced "wiggling" to loosen her up, she felt she'd made contact with the person inside the performer. Finally, the song came alive, quietly and surely, the notes on the page dissolving into irrelevance.

The process was repeated again, with minor variations, for a lanky tenor, Michael Kelly, and a lanky bass, Matt Boehler. (Jennifer Sheehan, a soprano who had the most natural delivery, was quickly dispatched with appreciation and a few more modest tips.) Both were made to sing their songs not to the audience as a whole but to a particular person, a technique as simple as it was efficient. The audience, engaged by the process, eventually got into the act. When Ms. Cook seemed stumped about how to get Mr. Kelly to loosen up and deliver his chosen song, the Odgen Nash-Vernon Duke tune "Low and Lazy," someone finally called out what I'd been itching to say: "Get him out of that suit jacket and tie!" She did; he blossomed. (I would have added that the lyric's humor was being sorely overlooked, too.)

But the most arresting moment came when a svelte redhead named Ariana Wyatt came onstage. Radiating charm and confidence, she began to sing a little-known Gershwin song called "In the Mandarin's Orchard Garden," about a misfit flower. Ms. Cook clearly wanted to find the woman behind the poise. She tried the same techniques she'd used on the others, but still Ms. Wyatt seemed intent on delivering a perfectly manicured performance that was just what Ms. Cook didn't want to hear.

As frustration mounted on both sides, Ms. Cook finally turned to face her student and said, with real sincerity: "You are a beautiful young woman. You have a beautiful voice. You don't have to prove it to anyone." Ms. Wyatt nodded, and a couple of tears ran down her cheeks.

I'm afraid those words are paraphrased. The pen stopped moving when the heart stood still. Although it was not part of a performance, the moment may well linger as one of the most moving things I've witnessed in a theater. Ms. Cook dabbed the tears away, then watched a little dumbstruck as her student insisted on leaving the stage for a moment to gather herself. "This is a first," she said a little sheepishly.

And what had happened? It's hard to say. Maybe, in the unlikeliest of contexts - on a public stage - two people made a brief but meaningful connection. Certainly, an established artist gave a small gift of assurance - of love, even - to an unformed one. The serenity of age looked back at the insecurity of youth, which marshals technique and posturing to defend itself, and said, try to let it go. You don't need it. You are enough.

Ms. Wyatt returned to the stage, determined, and sat down, and sang. She was still riven with emotion, maybe a little too much. Ms. Cook asked her how it went. It was harder to sing this way, Ms. Wyatt confessed. Ms. Cook said it would get easier. The audience applauded her enthusiastically, wanting to honor both the progress she'd made and the discomfort she'd endured to get there.

Class was dismissed after Ms. Cook practiced what she preached, performing "A Wonderful Guy" according to the simple precepts she'd set forth. But Ms. Cook's artistry is so pure it's hard to see what's behind it. It was the work we'd witnessed that illustrated the simple but profound insights behind her philosophy.

When performers first step onstage, they may be looking for validation, for approbation in the form of nourishing applause. But the lesson Ms. Cook came to teach was that artists achieve their peak when they learn to stop proving themselves and simply, to borrow the Shakespearean phrase, let be. It's their humanity we respond to in the end, their ability to strip away the self-consciousness that locks us inside ourselves, and reveal the stuff that really boils in our souls.

Talent is necessary, training is important, but they'll only get you halfway to becoming a real artist. For directions on the last, hardest stages of the journey, see Barbara Cook. Any time you can.

~by Charles Isherwood, New York Times