Postmodernist film is a classification for works that articulate the themes and ideas of postmodernism through the medium of cinema. Some of the goals of postmodernist film are to subvert the mainstream conventions of narrative structure and characterization, and to test the audience's suspension of disbelief. Typically, such films also break down the cultural divide between high and low art and often upend typical portrayals of gender, race, class, genre, and time with the goal of creating something that does not abide by traditional narrative expression. Modernist film came to maturity in the era between WWI and WWII with characteristics such as montage and symbolic imagery, and often took the form of expressionist cinema and surrealist cinema (as seen in the works of Fritz Lang and Luis Buñuel) while postmodernist film – similar to postmodernism as a whole – is a reaction to the modernist works and to their tendencies (such as nostalgia and angst). Modernist cinema has been said to have "explored and exposed the formal concerns of the medium by placing them at the forefront of consciousness. Modernist cinema questions and made visible the meaning-production practices of film." The auteur theory and idea of an author creating a work from their singular vision was a cultural advancement that coincided with the further maturation of modernist cinema. It has been said that "To investigate the transparency of the image is modernist but to undermine its reference to reality is to engage with the aesthetics of postmodernism." The modernist film has more faith in the author, the individual, and the accessibility of reality itself (and is generally more sincere in tone) than the postmodernist film. Postmodernism is in many ways interested in the liminal space that would be typically ignored by more modernist or traditionally narrative offerings. Henri Bergson writes in his book Creative Evolution, "The obscurity is cleared up, the contradiction vanishes, as soon as we place ourselves along the transition, in order to distinguish states in it by making cross cuts therein in thoughts.