You can have the greatest play in the world, the finest symphony, the most brilliantly performed opera, but the one element no actor or producer can control is the audience. Without it, there is no event, but trying to figure out what makes an audience enthusiastic one night and dead fish the next is a game of unending mystery for performers.

"I was taught that it's always the performance to blame and never the audience," said actor Floyd King, a key member of the Shakespeare Theatre at the Folger company. "But I've come to think that's not always true." King is playing Parrolles in "All's Well That Ends Well," and some nights, he said, "they start laughing immediately, and we haven't done anything, so you know it has nothing to do with us."

Many performers start out thinking of the audience as a great black blob with fangs, but as they gain experience view it with more empathy. But there's still a tendency to see the audience as an "it," a single entity that is either involved or obnoxiously silent, coughing, rattling or reading programs, snoring, talking to a neighbor, singing along, or, in some rare cases, drunkenly announcing a need to use the restroom or even vomiting on the customer in front and then settling back to enjoy the show.

"They are a little like children," said French singer Franc ois Loup, now playing the role of Mustafa in the Washington Opera's production of "L'Italiana in Algeri," "they expect to receive something and if you don't give them for what they came they can get ugly."

Loup, being from Europe, has witnessed audience behavior there that is unheard of here except in some notorious rock concerts. About eight years ago, he recalled, an English director aroused the wrath of French opera singers by hiring only English performers for a production in Nancy, so several hundred of the disappointed French went to a performance expressly to sabotage it with vehement booing. Italian audiences have been known to stop a production for half an hour with catcalls and foot stomping when the announced star cancels at the last minute. Or to pelt the stage with vegetables.

At a children's theater performance of "The Wizard of Oz" in Montana, one small boy nearly wrecked the show when he greeted the entrance of the witch by saying 'There's the witch, let's get her,' and then 50 kids chased the hapless actress out of the building. Usually an audience's response is not quite so visceral. But how is it that they can be so different?

No one knows. But there are a few guidelines -- myths, perhaps -- that performers seem to hold true. For example:

Saturday night audiences are the worst in the theater. "We always blame it on them having been overfed and overwined before they come," said veteran stage manager Mitch Erickson. "In our theater, they're more likely to be coming because it's a social event," said the Folger's King. "While someone who comes to see Shakespeare on Tuesday you know is there because he wants to be, not because it's date night."

In the music world, on the other hand, Saturdays are good nights. "They know they have a day off the next day so they are in a good mood," said Loup. Weekdays are often worse, he said, because "they wanted to come on a Friday or Saturday but all they could get was Monday. We have the feeling sometimes they are tired."

Matinees tend to be mostly women or older people and therefore react somewhat differently. "They enjoy it and we feel often they have been touched, but we don't expect them to be wild and screaming," said Loup.

Audiences made up largely of a benefit group can be deadly. "A lot of them are there not because they wanted to see that particular show but because their husband or wife is hooked into a certain charity," said Erickson. "Unless it's an Actor's Fund benefit; then it's your peers."

Performances during the holiday season are either great or deadly. "If they're down we say they're tired from shopping, and if they're up we say they're in a holiday mood," said King.

A small house can affect both the audience and the performers. "I once went to see a performance of 'Sugar' on Broadway with Robert Morse," King recalled, "and there were only about 30 people in this giant theater. And he performed as though it were full, and we loved it. That really inspired me."

With a comedy, a small house can be particularly devastating, because laughs become part of the play's rhythm. But the pros know that trying to compensate for the lack of audience volume by working harder for laughs always falls flat. Sometimes they try to think of other things.

"Toward the end of the run of 'Play It Again, Sam' the houses had started to fall off a bit," said Erickson. "So Woody Allen started this sort of game with the house manager. He had him come backstage after the show to give him a count, but tried to guess it before. He got to be incredibly good at guessing how many people were out there from the sound of the laughter."

There is usually a point in the show where you can tell whether you have them or not. Opera singers judge partly by the number of ovations. "Almost always at the first curtain, you have a kind of breeze, and you can know if they love you or hate you," said Loup. "It's a kind of electricity."

In "Shear Madness," a farce playing now and indefinitely in the Kennedy Center's Theater Lab, the audience has been described as the seventh character because it actually participates in the show. The actors can tell almost immediately whether the crowd is local or tourists, said director, coproducer and performer Bruce Jordan. "At the beginning I say, 'Can you believe this weather we're having,' and the cop says, 'This is nothing like where I grew up, in the country,' and I say, 'Oh, where was that?' and he says, 'Hyattsville.' Well, if they laugh at that we know they're local and know that Hyattsville isn't in the country. But if the place is bought out by an IBM group from Webster, New York, like it was one night, then you get silence."

There is almost no correlation between the audience's response and the performer's perception of how it went.

"John Wood is famous for saying, 'omigod, you didn't see it tonight,' " said Erickson. "And he's just dazzled you with brilliance."

Jordan recalls watching his replacement in the Philadelphia company of "Shear Madness," and thinking the actor was so bad "I was humiliated that anyone would think I had any connection with the show. I took all these notes, and during the intermission these two darling ladies came up to me and asked if I had anything to do with the show. I told them, and said that I had also played the part of Tony Whitcomb. And they said, 'Well you couldn't have been any better than this man.' And that's what theater is, it's what they see on that one night."

But the audience is not always right, even if it is always honest, say some performers. "An artist can fool an audience," said Loup. "Some artists use charm to convince them they are good. Or an excess of vocal power or overacting will sometimes work. Sometimes a director will do crazy things onstage and people say it's wonderful because it's like TV, with bright colors or a lot of guns and noise."

"I trust only me," said Tana Hicken, a member of the Arena Stage company who is now playing the lead in "Light Up the Sky." "I know when I am totally in control and when I'm not. But as the run goes on, the degree to which you are off on a particular night is very small."

Kim Stanley, recalled Erickson, would say she gave only two or three performances a week that pleased her. "But to the layman she was wonderful, and she was willing to say that maybe she was."

Fighting back doesn't work. There are times when a conductor, a singer or an actor is so peeved by obnoxious audience behavior that he or she will try to change it. Conductor Lorin Maazel once held the start of a concert until the coughing and shuffling subsided, recalled National Symphony bassoonist Ken Pasmanick, and Thomas Beacham actually sat down on the podium and put his head in his hands in annoyance at some late comers.

Katharine Hepburn was notorious for stopping "West Side Waltz" when someone ignored the ban on taking pictures during the performance. "I was at a performance when she stopped the show and announced the ushers would be coming down the aisle to confiscate the camera," said Erickson. "Of course no one admitted to being the guilty party. Then she started the show again from the top, and the adrenaline was so high they just screamed with laughter. They were on their best behavior."

Erickson was stage managing a performance of "The Iceman Cometh" here when Jason Robards became so annoyed with a man in the front row following the play with a script in which he was noisily making notations that he asked Erickson to make the man change his seat. It turned out the theatergoer was working on a thesis about Eugene O'Neill and noting each laugh. Since one of Robards' goals as an interpreter of O'Neill is to downplay his reputation for heavy drama and play up his comedy, he was chagrined at having chastised a scholar with a like mind. But Robards still wanted him to move, and he did.

Frank Grimes, an Irish actor hired by the Folger to play Hamlet a couple of years ago, stepped offstage, grabbed an offending program out of a man's hand, and ripped it up, so annoyed was he at the fact the viewer was reading it. "The audience applauded this behavior, which I hated," said King. "If you're boring them, what can you say?"

The late James Coco once told a story about an audience he had during the run of "Last of the Red Hot Lovers" that seemed terribly quiet. He got an enormous ovation at the end, however, and later learned they were deaf and had been reading his lips during the show.

"You should never get into a fight with the audience," said King. "They always win."

There are differences in audiences not only from night to night but from city to city. Washington, despite the feeling of some that we will give a standing ovation to anything that walks onstage, has a reputation for being more sedate than some other cities.

"The reason is in cities like San Francisco and Chicago you have many children of Italian immigrants who are starved for opera," theorizes Loup. "When they like something they are screaming. Washington is more English, richer and more behaved. They think it's a good thing to see an opera. Often after the first bow a couple will get up and find their way out because they want to get their car out of the garage. This is very discouraging. I have done about 100 performances here and I don't remember there ever being more that two or three minutes of applause. But in San Diego, for example, they really went wild. Maybe the weather is better."

There seems to be no way to change people more worried about getting their cars than enjoying the show, aside from giving everyone a number to order their exits. But some performers make a point of remembering that the audience is not their enemy -- at least not when the show starts.

Hicken, a professional actress in resident theaters for 20 years, makes a point of looking at the audience, unseen, before her first entrance. "If I go out and think about how I am going to reach them, it makes the theater seem smaller," she said. "I make them my friends. Then I can't wait to get out there."