One of the pay-offs of doing a goodly amount of reviewing lately has been the opportunity to see my craft from a different angle — to look under the hood, so to speak, and watch the machinery whirl away.
One of the pen-nibs all playwrights use, at some point, is exposition — that seemingly important presentation of data that the writer believes are essential for the audience to "get" the meaning of the play. A couple of forms of exposition get used. One is the informing kind, such as a list of kings in a historical play or "news flashes" between scenes to set a time-context for the action. The other is "backstory," a character's psychological CV presented to explain behavior or justify action. Both kinds of exposition are essentially historico-psychological in nature, bringing something that's already occurred to bear on the present and future of the play's characters.
I've found that exposition is usually done badly — that is, you can hear the wind-up and pitch of it immediately: "Do you remember when we...?" or "Explain the argument to me again" or "I don't understand" or (as an action onstage) "Let me read this letter out loud that I'm handwriting." The writer's purpose is obvious: I believe that you will need this information in order to have a critical understanding of the play.
What is not so easily proven is that the audience actually uses the information in this way, or even uses it at all. I know I usually don't, for several reasons. First , the action of a good play is forward — there is no time to pause, reflect, apply, conclude. (Perhaps after the play, at a drink or dinner, and maybe during intermission, but certainly not in media res.) Second, it's usually not necessary. If there is an explosive dramatic nugget at the core of the piece, there is no real need for a visit to the past or a review of a list of "why's." The issue at hand, in the present tense, should be sufficient to hold our interest. Third, characters are not people — they are devices we use to tell a story, no different, in essence, from light, sound, set design. I don't mind, in a play of mine, if an actor wants to supply a backstory to a character, but I generally do not, at least as an actual working part of the script.
This doesn't mean that I don't have a past tense in my plays. It means that I try to make anything like exposition part of the dramatic flow. I never want an audience member to suddenly feel that wind-up-and-pitch of the expository delivery. As much as I can, I banish phrases like "Do you remember?" and "Well, in 1943, in Beirut..." This makes writing a script much more difficult — pleasantly so, because it demands that I become inventive about how the story's information slips over the stage's apron and into the audience.
For instance, in a piece I'm working on now, one of the characters is a bioengineer creating a new process for studying brain function, called "optogenetics." The other is a philosophy professor at the end of his existential tether (not a bad place, really, for a philosopher) who wants in on the upcoming human trials of the process. The challenge is to tell the audience about optogenetics without letting loose the odor of exposition. The prof has a touch of the histrionic about him, so I have him sing (to the embarrassed but intrigued response of the bioengineer) a hymn to optogenetics. It gets out the info the audience needs to understand the process but does it (I hope) in a more theatrically interesting way, in a way true to the character and without using a stale trick like the bioengineer giving a lecture, with the audience as students (a device used recently in a play I reviewed titled "Sweet Sweet Motherhood").
In order not to bore or distract an audience, all exposition needs to be folded in to dramatic action — one should get the information without ever feeling that it has been delivered or ladled-out. And just enough is the right amount — audiences are always less interested in the information than they are how the information warps the dramatic space-time continuum around the characters and their struggles to come to grips with something about life, liberty, and the pursuit of happiness.