Theoretical background

Film theory tries to justify and explain the jist and systematic principles of film as art. The initial theoretical background was provided by David Hume (as it was above said) in the middle of the 18th century, but it was not enough. There was a necessity to explain the origin of screen films and close ties it establishes with global audience.
The first real report was created by Ricciotto Canudo that was named "The Birth of the Sixth Art". Soon afterwards, Rudolf Arnheim, Bela Balaz and Siegfried Kracauer founded formalist screen film theory. Its main principles stressed the fact that cinema and reality are two different things, referring to screen films as one of the Fine Arts.
As a normal fact, there were a lot of other theories and protesters that claimed screen films being able to render reality what caused the emergence of realist theory.
So, till the 1920s there existed two main screen film theories, that is formal and realist. The flourishing of the 1920s gives rise to a lot of other hypotheses. What's more, film theories were influenced by the discoveries and principles in other fields and domains of science and art.
In particular, the general film theory was influenced by Lacan's psychoanalysis and semiotics by Ferdinand de Saussure.
Starting with the 1920s, there appears a great number of contigious theories, among which the most important were structuralist film theory, feminist film theory and many others.