In this extremely helpful little video clip, South Park creators Trey Parker and Matt Stone share the rule they always follow to make sure that their structure is sound and all of their scenes serve a purpose.
Put simply, if you’re looking over the scenes of your script and you can’t reasonably say either “BUT” or “THEREFORE” between each and every one of them, then you’ve got a problem. If all you can muster is an “AND THEN,” you’re not progressing your story.
Now you could argue that some of the greatest films, like Boyhood, don’t follow this rule. But I would argue that Boyhood isn’t so much a movie as it is a cinematic experience — and a glorious one at that. In short, if you’re writing a story with a three act narrative structure, you should always be able to say either BUT or THEREFORE between each and every scene.
Visit the Academy of Film Writing for more videos like this one.