It’s as if a one-man show about Van Gogh were performed by a guy who could paint, or one about Nureyev showed off an actor who could turn a mean jeté. Hershey Felder, creator and purveyor of George Gershwin Alone, is also a concert pianist, so when his Gershwin is moved by the musical spirit, there’s none of that twiddling of fingers over the keyboard to piped-in piano. Felder sits down at the Steinway to illustrate a passionate music lesson or an equally fervent self-endorsement with the actual goods. And from " Swanee " to the emotion-drenched love duet from Porgy and Bess, they speak for themselves. Gershwin’s own playing was more buoyant and less aggressive than Felder’s. Still, the performer is a classically trained musician as well as an actor.

Felder’s somewhat pretentiously subtitled but musically dramatic " imagination with music " was developed at the Tiffany Theatre in Los Angeles, where it was a runaway hit, and went on to a 2001 stint on Broadway. It’s being hosted here by the American Repertory Theatre, which takes advantage of Felder’s happening to be in Cambridge while his wife, former Canadian prime minister Kim Campbell, teaches at Harvard’s Kennedy School of Government. Felder too is a native of Canada, but that doesn’t stop him from immersing himself in the son of Russian immigrants who, when asked in 1925 by Vanity Fair to imagine an epitaph for himself, penned the following: " Here lies the body of George Gershwin, American composer. Composer? American? "

This quip homes in on one of the paradoxes at the core of Felder’s presentation, the program notes for which quote Abram Chasins’s melting-pot description of Gershwin: " The language he spoke was an eclectic one — black-face humor, Russian sentimentality, Jewish sorrow, Broadway pep, and French ooh-la-la. In short, Typically American. " The other contradiction central to the piece is also its dramatic Achilles’ heel. This show presents its subject as a somewhat stiff, guilelessly egotistical figure whose deep emotions and enthusiasm surface only in the music. Although Felder’s Gershwin expresses a tender admiration for his brother, master lyricist Ira, he’s so busy obsessing over the score of Porgy and Bess that he lets orchestrator and lady love Kay Swift slip between his ivory-tickling fingers.

George Gershwin Alone finds the famed composer occupying what Felder calls " the apartment of his mind " — which was roughly modeled on Gershwin’s last actual apartment, on New York’s Upper East Side. As effectively designed by Yael Pardess, it’s a cluttered yet ghostly parlor where Gershwin is surrounded by family portraits and shadowy blow-ups of show music as he chats up the audience. We never understand exactly who we are, but then, we don’t really know whether our host is alive or dead since he does, in the end, narrate his untimely demise from a brain tumor at age 38 before " living on, " as it were, in Rhapsody in Blue, which he performs in its entirety. The wonderful music threaded through the theater piece only makes more poignant Gershwin’s frustration, despite his early fame as a songwriter, at being slighted by highbrow critics unable to reconcile jazz with serious music. (And jazz, as is made chillingly clear in a racist, anti-Semitic Henry Ford screed quoted here by a devastated Gershwin, faced worse prejudice than that.)

As an actor, Felder is serviceable, and sporting a snug double-breasted suit and slicked-back hair, he resembles the Gershwin who occasionally looms in projection behind him. Moreover, he creates a melancholy if wry persona for the composer, laying out the biographical tchotchkes in more or less chronological order. But the character comes most to life in channeling and explaining his music — demonstrating the minor-major key change that makes " Swanee " so catchy, or the honking auto horns he filtered into An American in Paris. Felder’s own persona, evinced in a sort of encore/audience-sing-along, is more playful. Director Joel Zwick, on whom the performer heaps fulsome praise, moves things fluidly and at a pace that reflects the composer’s blinkered intensity. Under his tutelage, George Gershwin Alone is a virtuosic turn. But the star, as intended, is not so much Felder, the devoted if somewhat strident acolyte, as the Muse who heard " music in the heart of noise. "