His works on the topic of screenwriting are considered to be the Bible of modern-day script structure.
Field is the author of eight books, mostly notably "Screenplay: The Basics of Film Writing," considered the the industry's most authoritative guide to screenwriting. It is credited with helping establish the now traditional three-act structure for feature film scripts.
Why I write and my experience...
Screenplay: in one word. Field's most notable contribution is his paradigm "three-act structure". In this structure, a writer sets a film's plot within the first twenty to thirty minutes. Then the protagonist experiences a plot point, providing the protagonist with a goal. About half of a movie's running time focuses on the protagonist's struggle to achieve this goal. The second act is called the confrontation. Field also refers to the midpoint, a turning point around the middle of the screenplay (such as on or around page 60 of a 120-page screenplay). This turning point is often a devastating reversal of the protagonist's fortune. The third act depicts the protagonist's struggle to achieve (or not achieve) his or her goal, as well as the aftermath.