Think of the theme of your screenplay as something the main character has to learn. Traditionally, they believe the opposite, then learn the lesson represented by the theme.

What is the essential question your movie is asking? Make your theme a declarative statement. The answer to that question.

One of my favorite examples of theme and anti-theme is in the recent Murder on the Orient Express. In the first act, Poirot states his world view. “There is right, there is wrong. There is nothing in between.” The anti-theme, because…

Poirot then spends the movie investigating a crime that puts his view to the test. By the end, he admits to himself that sometimes murder is justified. He comes to believe there IS a place between right and wrong, and acts on that belief.

So the essential question, “Is there a gray area between right and wrong?” is answered as “Yes”. The theme as a statement would be “Sometimes, murder can be justified.”

When I looked up this scene online, I found the dialogue quoted on IMDB (see below).

When I compared it to a PDF of the screenplay dated 2/20/15, I did not see that crucial line of dialogue. That tells me that the writer and producers at some later point decided that Poirot’s worldview needed to be spelled out more clearly for the audience. By doing so, it underlined the theme more clearly.