"the set-up, the placement of the crisis, the climax, and the denouement"

Film Kristin Thompson's book Storytelling in the New Hollywood was one of the key texts when I was writing my film studies dissertation because it's incisive explanation of how a screenplay is structured when considering the multiple stoylines in an ensemble movie. One of the films she considered was Groundhog Day and during the publication process, Harold Ramis was contacted to offer a blurb for the cover. He sent back a letter which Kristin has posted on her blog as a tribute. It's really interesting:

"I am not a student of screenwriting so I’m afraid I can’t comment intelligently on Ms. Thompson’s theoretical model. Certainly, the fact that most movies are about two hours long will determine to a large extent the length of the set-up, the placement of the crisis, the climax, and the denouement, but rather than look at films in terms of “acts,” I prefer to think in terms of “actions,” as if the narrative line were a string of pearls, dramatically linked, each taking the audience forward to the next point. If any particular action doesn’t advance the plot or contain some new information, it doesn’t belong in the narrative. As a writer I generally proceed more intuitively than structurally. As Ms. Thompson suggests, I suspect that most of us have simply absorbed the classical film structure during our formative years as members of the audience."

Kristin mentions as much in her book, which also includes a section which looks at less successful films to see if it's because of the structure and quite often it is and the eventual conclusion is that it's an alchemical mixture of the two elements - filmmaker's unconscious intent and the "rules" and how they'r extrapolated. It's worth noting though, that once you have this four-part structure in your head, you'll always intuitively know when each turning point is going to be in a film and in the very best, it's always almost exactly at 25%, 50% and 75% of the running time and the contents of each .... see above ...