Theatrical dialect coaches believe that in an actor's creation of a character, the talk has to precede the walk - or, if you're a Jersey boy, the "tawk" precedes the "wawk" - especially if you're going to sing a "sawng." And that means you need a dialect coach.

Dialect coaches are like Henry Higgins, the phonetics professor from Shaw's Pygmalion and, later, Lerner and Loewe's My Fair Lady. They can tell where you're from at the drop of a consonant.

Jersey Boys, the popular musical about Frankie Valli and his guy-group the Four Seasons, has been workin' its way back to us, babe, on national tour, and opens Thursday for a month at the Forrest Theatre, its third visit in four years. And the Jersey boys have to sound Jersey - especially so close to home - so the production called in Stephen Gabis, a dialect coach whose job is to make these actors sound like the real deal.

Talking to Gabis on the phone was entertaining but essentially unprintable: He reeled off big chunks of dialogue from the various Broadway shows and Hollywood movies he's worked on, speaking in different dialects, nimbly switching from Irish to South African to New York. But unless this article were to be written entirely in phonetics, it's hard to figure out a way to convey most of what he said.

(Gabis did mention the basic linguistic terms "rhotic" and "non-rhotic," which refer to whether you say your "r"s: butter vs. buttah. In the 18th century, the British started dropping their r's, and that migrated to America, and that led to "New Yawk." And New Yawkers migrated across the river to New Jersey, and that led to Frankie Valli.)

Marcia Hepps came to the rescue: An actor and local dialect coach, she is also a professor at the University of the Arts, where she teaches dialects to student actors. As a teacher, she knew how to explain what was what.

Here are the basics:

An accent is the way someone speaks a language not his or her own (a Frenchwoman speaking English with a French accent), and dialect is the way someone speaks his or her native language.

All people have a dialect, Hepps says, although all people think they don't; infants are born with a dialect, and toddlers will always respond to a stranger who speaks with their dialect, as opposed to one who does not: linguistics is tribal. Babies cry in dialect: A French child's crying is discernably different from an English child's. The ear acclimates in the womb.

If an actor grew up watching Rocky and Bullwinkle, a Russian accent will be easy; if he grew up watching Bugs Bunny, Brooklynese will be easy.

One of Hepps' lessons is variations on "vampire dialect" - the difference between Bela Lugosi and the Count on Sesame Street.

Dialects and accents depend on where the voice is placed in the mouth. The Jersey dialect is spoken at the back of the front teeth, while the Russian accent is farthest back, almost at the jawline, and the Irish is as far forward as possible, almost like blowing out a candle.

There are "cool" dialects: In the 1980s, it was Valley Girl and Surfer Dude; then came hip-hop; students now say the new dialect is "text"(!). In England, Gabis told me, young people tried to sound like the Beatles (the Liverpudlian dialect is called scouse), but now they want to sound Australian.

Hepps laments that so many dialects are being lost as the world becomes more global and as the media erase linguistic origins. In Britain, "R.P.," short for "received pronunciation," is a standardized English nobody except actors speaks, just as in the United States, "GenAm" - General American - is a homogeneous, poshed-up version of Midwest/East Coast English. In other words, the dialect of no place.

A recent book by David Crystal, Pronouncing Shakespeare, explains that for Shakespeare, "love" and "prove" rhymed, significantly altering the rhythm of the plays. And apparently, Shakespeare's English was much closer to the English now spoken in Appalachia than in Buckingham Palace.

Like a latter-day Henry Higgins, Princess Diana knew dialect was the key to how people responded to you, especially in England, and her great project was to teach underprivileged children to speak a cross between R.P. and cockney, what we would call "street." This amalgam is now known as Thames Estuary, referring to the outer reaches of London defined by the river.

It's not just where and into what economic bracket you were born that determines your dialect, but how you identify. There is nothing politically correct about dialect, Hepps notes: "It's all stereotype." This can make dialect coaching controversial, as, for example, the "gay" dialect (with its sibilant s). There are "stupid people" dialects: in America it's Deep South, in England, it's Scottish.

A dialect coach, Hepps says, is like a lighting designer: the work should not call attention to itself, but become "part of the fabric" of the show. (Consider, for example, on TV's The Good Wife, how completely New York Jewish Alan Cumming sounds, while his natural speech is deeply, nearly impenetrably Scots.)

So, the next time you "pahk your cah in Hahvahd Yahd," you'll know where you are. Or, if you're from Jersey, where you're at.

THEATER

Jersey Boys

Through Jan. 5 at the Forrest Theatre, 1114 Walnut St.

Tickets: $40-$127

Information: 215-893-1999 or www.kimmelcenter.org EndText