"What if?"

Playwrights can build entire dramas on those two words. Truth may be stranger than fiction, but fiction trumps fact when it comes to emotions.

Take two current examples: What if Mary Stuart and Elizabeth I had a real heart-to-heart? What if Scott Joplin and Irving Berlin actually worked together?

In "Mary Stuart," the explosive revival of Friedrich Schiller's drama now in its final Broadway weeks, the two queens have a last-ditch confrontation that's both chilling and fiery, telling us much not only about their personalities but the world at large.

In "The Tin Pan Alley Rag," playwright Mark Saltzman tries to remedy the fact that Joplin and Berlin, despite being on parallel career paths, never met, an unfortunate non-event considering their pop culture influence. In Saltzman's play with music, Joplin and Berlin do meet, spilling their sorrows about the early deaths of their wives and regaling each other with snippets of their songs. Both composers were into ragtime, the syncopated beat that, along with jazz and musical comedy, represents the most indigenous American music. (Joplin's "Maple Leaf Rag" and Berlin's "Alexander's Ragtime Band" are still played.)

But the result, sad to say, is a diffuse, heavy-handed dead end. The songs are pleasant, the performers apt, but the staging is awkward. Saltzman needs a dramaturge, someone to ask hard questions like "Just what is it you want to say?" The play is heavy on exposition and explanation, leaving us with one-note character development.

One idea that comes through is that pitting Berlin against Joplin is pitting commerce vs. art. "I started writing songs to get rich," says Berlin. When the classically trained Joplin compliments Berlin, who can't read music, as "a born musical genius," the New Yorker replies he is really "a born hit maker." And so he was, turning out success after success while Joplin wants nothing more than to see his opera "Treemonisha" performed.

The irony is that both men captured the pure American spirit. Joplin's Afro-American rhythms counterpointed Berlin's Jewish Mittel European ones. Out of their talent was forged a new sound, black and white, male and female, classical and popular. In the production, songs are not just mentioned; they're also nicely performed. Yet, except for a compelling scene between Joplin and a classical conductor, "Tin Pan Alley" is more leaden history lesson than forward-driving drama.

Of course, you'd expect a history lesson from "Mary Stuart," but author Schiller twists facts to show women struggling to make their mark in a man's world. When Mary and Elizabeth finally face each other, the meeting, which never actually happened, builds to such intensity that the playhouse seems too small to contain them.

Taking only their cues from history, "The Tin Pan Alley Rag" and "Mary Stuart" dig for feeling, not fact. But the former's facts stop at the door, while the latter's allows light to shine on the emotional truth of a pair of towering figures.

"The Tin Pan Alley Rag" is at the Laura Pels Theater, 111 W. 46th St., N.Y., through Sept. 6. Call (212) 719-1300 or visit www.roundabouttheatre.org.

"Mary Stuart" is at the Broadhurst Theater, 235 W. 44th St., N.Y., through Aug. 16. Call (212) 239-6200 or visit www.telecharge.com.