The job of the actor is to activate material, whether it's a monologue or song (which is essentially a heightened, stylized monologue).
Opera, with its emphasis on vocalism above everything else, is a science, demanding a cultivated vocal precision from its practitioners and an adherence to the score, even at the expense of dramatic credibility. Watching the obese Jane Eaglen pathetically struggling to execute the simplest staging while gloriously negotiating the vocal demands of Wagnerian opera is a case in point.
Musical theatre, however, places greater emphasis on the coherent dramaturgy of its script, with its songs, arising from the text's narrative action and character. The well-written musical extends its action through the songs and provides the actor with something to play throughout the song and, as an art, allows a greater leeway of interpretation and psychological nuance. Hence, it requires performers who are able to negotiate the vocal demands of the music as well as provide credible motivation, subtext and behavior in their delineation of character.
The canard that "musical theater actors stop acting when they start singing" is a long-outmoded prejudice from the days when musicals had librettos with flimsy constructions, ludicrous situations, and unbelievable characters (the sit-coms of their day). That attitude is fostered today by ignoramuses, be they directors or casting agents, who have no understanding or perception of the nature of musical theatre in the first place. Singing actors like Donna Murphy and Malcolm Gets, to name two, are exceptionally talented singing actors who leave such notions behind in the dust.
Of course, there are roles like Billy Bigelow or Momma Rose which have come to be associated with a certain vocal prowess. Needless to say, there is a sense of diminished expectations or disappointment when less-than-stellar vocalists essay those roles. Yes, I would have preferred Tyne Daly to soar on the "I-I-I-I at least gotta try" bridge of SOME PEOPLE and Michael Hayden to rise to the vocal heights in the SOLILOQUY. But, nonetheless, there were other pleasures to be found in both of their well-acted performances that perhaps eluded their predecessors. And, in case someone thinks they don't make performers like they used to, I suggest you listen to Gertrude Lawrence in any number of performances available on record. For all her charisma and magnetism, she had one of the most unreliable singing voices ever, thin and poorly-intoned on most occasions. But none of that seemed to matter due to her great glamour and appeal.
Updated On: 8/24/04 at 10:27 PM