Michael Rabiger (2009)¹, a professor and academic specialising in documentary studies, gives a helpful and succinct summary of the three-act narrative structure:

• ACT I: establishes the setup (characters, relationships, situations and the dominant problem faced by the central character/s
• ACT II: escalates the complications in relationships as the central character struggles with obstacles
• ACT III: intensifies the situation to a point of climax or confrontation, which the central character then resolves, often in a climactic way that is emotionally satisfying

The name given to this collection of changes and developments is the dramatic or story arc, and each individual moment of change is called a beat.

I still struggle with the idea that rigid structures like three-act narrative are necessarily good. My natural inclination is to suspect that such formulaic progressions are used not just as vague guides but as templates that actually hinder the development of interesting or new stories. Indeed, some of my filmmaker friends seem entirely wedded to the idea that particular story beats must occur at certain points in their script.

But basically all of the films it’s possible to see in mainstream cinemas today, even those I would consider “unconventional”, are still governed by three-act structure even if the structure is not immediately identifiable. The only films that truly eschew traditional structures like these are the genuinely experimental films of filmmakers like Stan Brakhage, Chris Marker and Maya Deren.