Ideal Structure of Screenplays

Blake Snyder's book Save the Cat gives one of the best breakdowns of what makes a screenplay fantastic. His structure is one I intend to use to analyze the writing in films so here is a breakdown of Snyder's film structure with terms, which can be found in Chapter 4 "Let's Beat it out" of Save the Cat, and my summary of their definitions:

Act 1:

1. Opening Image - this is the attention getter, to make sure the audience right from the start is interested in the story that is about to unfold. 
2. Theme Stated - Snyder believes the theme needs to be given to the audience right away
3. Exposition - any essential information that the audience needs right away. This is tricky because past information cannot always be given to the audience in a way that is natural to human behavior. 
4. Catalyst - Snyder's guide suggests that all films require a catalyst, that is a change from past life to new life. 

Act 2: 

1. Break Into Two - this the point at which an essential choice is made and this choice propels the action of act two
2. Midpoint (False Victory) - either the main character succeeds or fails, but both appear to be failures. If he succeeds he soon discovers that this is not exactly what he wanted.
3. Bad Guys Close In - Villains have a sudden boost of energy and defeat the hero's goal
4. All is Lost - Anything the character gained over the timeline is suddenly all lost
5. The Dark Night of the Soul - Main character hits a dark point of hopelessness and mourns whatever has 'died' (either dream, life goal, persson, etc). 

Act 3:

1.  Break Into Three - sage advice or a strange pull of courage makes the main character try again 
2. Finale - character then understands the theme of the film for himself 
3. Final Image - last image that confirms a change has occur

This is just a basic rundown of Snyder's description of the moments of plot or story that seem statistically common in most films. Not every film is going to follow this charted course, and willful deviations from this can carry artistic themes in itself. If you are interested in writing screenplays I definitely suggest you read Snyder's book.

Snyder, Blake. Save the Cat!: The Last Book on Screenwriting You'll Ever Need. Studio City, CA: M. Wiese Productions, 2005. Print.