Let me start by pointing out that I’ve never written a screenplay myself. I’ve read some, and I’ve worked with some doing novelizations, but that’s a bit different from writing them myself.
I feel the need to point this out because I keep running into folks who think that because I write novels, I can advise them about their screenplays, either generally (“How should I write a screenplay? Who do I send it to?”) or specifically (“Could you critique this screenplay for me? There’s something wrong with this scene…”). There is, of course, a certain amount of overlap in the storytelling and structural aspects of both disciplines, so I can occasionally be helpful. But these kinds of questions always worry me just a little, because the people asking them are ignoring two really fundamental and vitally important differences between the two crafts…and as a result, they often make mistakes that can seriously muck up what they’re trying to do.
First off, movies are primarily visual, while novels are verbal.
Movies tell stories mainly with images. Have you ever been on a long-distance flight and not bothered to buy the headphones for the movie? I do it all the time, usually because I want to get some work done, and then I get distracted by the images…and son of a gun if I can’t tell at least 90% of what’s going on just from watching the pictures, no sound. Of course, they’re not meant to be watched that way, and I miss all the good lines and the ominous music and the creaking noise that alerts the hero just in time. Still, that seems to me to underline my point: movies tell the story with images, sounds, and dialog, and of those three, most of what the scriptwriter writes is the dialog part. (More of that in a moment.)
Novels have, for the most part, one tool and one tool only: language. Picture books include images as well as text, but the older the intended audience, the fewer illustrations tend to appear. By the time you get to YA novels, there’s hardly a picture in sight, and teen and adult novels limit illustrations to the dust jacket or cover (and even those are frequently abstract, rather than illustrative). In a novel, everything has to be done with words, which are processed in a linear fashion as the reader reads, right to left, one word at a time.
What this means is that a movie can make a huge impact with a single image. I still remember the first time I saw “The Wizard of Oz.” When the door swings open and the screen switches from black and white to color, and Dorothy (and you) get that first stunning glimpse of Oz…I don’t think anyone could duplicate that effect in prose. It would need a detailed description, and the more detailed it was, the longer it would be and the more time it would take…and the more time it took, the less you get that immediate stunning impact. On the other hand, the movie can’t give you Dorothy’s thoughts and feelings without an awkward voiceover, while a novel has little difficulty in providing a different sort of impact by going into her emotions when she realizes that she’s somewhere strange and far from hom.
The second fundamental difference between movies and novels is that all movies are massive collaborations, while most novels are solo efforts.
A movie is, at minimum, a collaboration between the writers, the actors, the director, the producer, the prop and costume people, the camera operators, the sound folks…all those people who get listed in the five minutes of credits that roll past at the end of the film. And note that I said “writers” – very, very often, a screenplay ends up being rewritten by a second or third writer, or worked on by a team from the very start. Novelists nearly always work alone. A scriptwriter is just the start of the process, and has little or no influence on what happens after the “final” script leaves his/her hands unless he/she is also directing or producing the movie. A novelist (or a team of collaborators) has ultimate veto power on whatever goes out in the final book unless it’s a work-for-hire.
Not being clear about these two differences causes problems for both types of writers.
I’ve seen screenplays where the writer kept inserting stage directions and notes to tell the actors how to say the lines or what the character is thinking at a particular time. Once in a while, this is necessary [GEORGE (sarcastically): That's a good idea!], but all too often, these directions betray the fact that the writer doesn’t really want to collaborate – he/she wants the actors, the director, the camera operators, etc. to make the exact movie the writer is picturing in his/her head. Furthermore, in concentrating on telling the actors and the director how to do their jobs, the writer often seriously neglects his/her own – writing dialog that tells the story without needing all those explanations of what the characters are thinking. Because, as I mentioned before, movies are notoriously bad at telling the viewer exactly what the character is thinking at any given moment. The camera can’t get inside the characters’ heads.
The scriptwriter also doesn’t necessarily know what is or isn’t available visually – what locations the director will be able to shoot at, what the budget will be for CGI, etc. Thus, the kind of detailed description of action scenes that you’d find in a novel are at best superfluous; at worst, counter-productive. Shakespeare does not say “A bear enters stage left, and lumbers threateningly forward. Antigonus sees it and flaps his coat to distract the bear from the baby. The bear turns toward him…” No, the stage direction is “Exit, pursued by a bear,” and that’s all.
This can seem very foreign to a novelist. I was horrified when I was given the script for Star Wars Episode I and found the Big Fight Scene at the end, which I knew was going to be at least five minutes of spectacular lightsaber fighting on-screen. The script said, in its entirety, “The Jedi fight.” That’s all it needed. (I, on the other hand, had to come up with several pages of description, because it was, after all, the Big Fight Scene At The End, and there was absolutely no way I could get away with “The Jedi fought.”)
By the same token, I see a lot of young would-be novelists struggling to duplicate in prose the kind of dramatic visual revelations, zoom-ins, close-ups, and other dramatic visual techniques that the camera in movies perform effortlessly. Sometimes, one can do something similar, or find a prose technique that has a parallel function. More often, the result is awkward at best, impenetrably awful at worst.
There are things that transfer from books to movies and vice versa, but if one is going to try, one really needs to begin by asking “Will this technique actually work in this other medium?”