That's a viola joke — and there are a million of them, say the violists of the New York Philharmonic.

Why?

Is it because of the instrument's shape and size? Unlike the more standardized violin, says Philharmonic violist Kenneth Mirkin, "there's no official size to a viola. You buy it by the inch."

How it is made?

It is an eclectic instrument. Principal Viola Cynthia Phelps, who sits front and center, plays an exquisite 16th-century Gasparo da Salo. Vivek Kamath plays a modern copy of a Guadagnini. Assistant Principal Irene Breslaw, the designated extra-string carrier for onstage emergencies, plays a 1930s Peternella. Kenneth Mirkin and Peter Kenote play custom-made contemporary models. Associate Principal Rebecca Young plays the largest viola: a 1619 Maggini. 'Tis a quirky mix indeed, down to the very wood from which they are made, of which there is much spruce and maple, with a dash of willow, poplar, and pear.

Its role?

Sir Thomas Beecham called it the "hermaphrodite of the orchestra," and Shakespeare evoked this gender-straddling in Twelfth Night in which his Viola disguises herself as a man. Larger than the soprano violin, smaller than the basso cello, it's the perfect inner voice. Accordingly, the viola rarely carries the tune. Instead, it supports, adds texture, and conveys the accompanimental figures that dictate rhythmic stability.

"We weave in and out, being showcased and then recede into the background," says Ms. Phelps. "There's an ebb and flow." Rebecca Young adds, "You don't shine on your own. You blend. Otherwise, you're sabotaging."

Offstage, the section's 12 fiddlers are also the consummate team players. In addition to their prolific chamber-music lives, many serve on the Philharmonic's orchestra committee, negotiating committee, artistic committee, tour committee ...

The depth of its voice?

Most violists start out studying its smaller sister, the violin, and then find a segue to the deeper instrument inevitable. Some felt "cramped" and "constricted"; others chafed at the treble edge. "The viola never screeches," murmurs Ms. Young. Its low, lush sound has seduced musicians for centuries, including Mozart, Mendelssohn, Bartók, and Hindemith, who played this instrument as well as composed for it. Ms. Phelps describes it as "dark velvet, very sultry, mellow." "Beefy," Mr. Kenote suggests, "with a nasally A string." "Chocolatey," says Mr. Mirkin. "Dark chocolate," adds Ms. Phelps.

But this sweetness has a price: stress on the shoulder, tendonitis, carpal tunnel, and clenched jaw are the hazards of maneuvering around such an elegantly unwieldy (or as Peter Kenote puts it, "flawed") instrument. Given its lanky build, its thick strings and strong tension, its long and heavy bow, the viola is famously hard to tame.

So why the jokes?

"Traditionally," says Kenneth Mirkin, "violists were failed violinists."

Now that's a joke.

Ellen Stern is a New York-based writer whose most recent book is Gracie Mansion: A Celebration of New York City's Mayoral Residence.