We all know the scripts that have dialogue that goes a bit like this:
"Who am I? I am your husband, her brother and that kid over there's father. We've been married for fourteen years, but your persistent amnesia dear wife has meant I have secretly been having an affair with your sister (that woman over there) and I fathered all seven of her children without you even having noticed. And by the way, can someone get me some coffee? I only like it black because that's the way I had in 'Nam, a place I will never forget: I was just nineteen years old, straight out of High School..."
This is expositional dialogue. Okay, the above is an exaggeration, but sometimes scripts can have chunks here and there and yes - they always, always stick out a mile. A bit like when Captain Jack introduced the team in the very first episode of Torchwood (though I did stick with that), or when whatserface's mother said, "Your husband, my son" in Heroes, thus turning off my attention forever. Apparently it got better after that but as I've said before, I have movie-TV-related ADHD. One my attention is lost, it's lost baby.
Thankfully, I don't see that many scripts with expositional dialogue these days: sure, there is the odd line here or there that states too much, but it's usually to do with early drafts and ironing various things out. I hardly ever see truly expositional lines in polished drafts anymore - not in the way I would see them, say, five years ago.
However, screenwriting issues are like Hydras it would seem: chop one off and another rears its head in its place. This new issue? Fatty Dialogue.
Fatty Dialogue still states too much, it tells it rather than shows it - but in a way completely different to expositional dialogue. I'll explain.
Fatty Dialogue is often really rather good. Characters will regale each other with amusing anecdotes or make withering observations about their colleagues. Characters will impress me with their knowledge of a certain topic, maybe I will even get a lecture about an important subject as a professor character gives his class a talk in a university. Maybe there will be strained, character-revealing small talk around the dinner table. The problem then?
The story doesn't need it.
Good dialogue turns to Fatty Dialogue when it adds nothing to the story you're telling. Often writers will want to include their meticulous research into a topic that fuelled their story, forgetting stories have what I call the "L'Oreal" approach: "Here comes the science!" In other words, you only need a little to impress, don't let it get bogged down in the ins and outs of the issue, scenario, etc. Jurassic Park did this well: "We can bring dinosaurs back to life from the blood a mosquito sucked out of them." Really? They managed to find mosquitos who had been encased in amber that not only had sucked blood out of ALL breeds of dinosaur, but out of every period of dinosaur history as well? Handy. But who cares! The story needs dinosaurs - here's some bloody dinosaurs.
However, because of Jurassic Park, Indiana Jones etc, I get loads of action adventures starting with lecture halls, slide shows or videos explaining how *the thing* came to be in the story. And these scenes will last ages. Three, four, five pages are not unusual. Often the Professor will have to field hostile questions - and whilst this shows what a great, clever guy he is, it's not really that interesting: why? Because we want the story to begin - and the only way he's going to really do that is by getting out of that lecture hall and actually engaging with what whatever the problem or issue is, rather than talking about it.
Similarly, writers like to show sometimes how lonely characters are - even whilst in the midst of a big circle of friends. This leads to characters having long conversations about stuff we know they haven't done in order to impress their peers; similarly we can see how dysfunctional a family is around a dinner table, whilst watching TV, on a day trip. However, if none of this feeds DIRECTLY into your plot, then it doesn't matter how great your dialogue actually is, it still turns to fat.
Dialogue is like scene description - it's not just about revealing character, it's about pushing the story forward too. Why would a character say something for no reason? Sometimes we have moments that are all about character, sure, no one's denying it: and that is great for style, such as Donnie Darko's rant about Smurfs. But all the time?!
We are all worshipping in the Church of Screenwriting Moderation my friends.