Hearing somebody say ‘The book is always better than the film’ is like fingernails down a blackboard to me. This ill-informed yet common cliché about the supposed superiority of literary texts over visual texts is highly reductive and suggests that a comparison can be made between two incomparable things. It leads to statements such as ‘Baz Luhrmann is going to ruin The Great Gatsby!’ Relax, people. He may make a film that’s not very good, and in the eyes of some he may fail to capture the spirit and ideas of F. Scott Fitzgerald’s classic 1925 novel, but unless the film’s producers have somehow arranged for every existing copy of the novel to be rounded up and pulped upon the film’s release, the novel The Great Gatsby is going to live on unharmed.

One of the main complaints levelled at film adaptations is that they change, condense or discard aspects of the novel. Now, unless you are arguing that novels should never be adapted into films at all, this is unavoidable – of course there are going to be changes made to the events and characters during the adaptation process. The average film, with a typical running time of 90 to 120 minutes, cannot accommodate every single element within a novel. While some plot points may be objectively crucial to a story, there are an enormous number of other elements within a novel that can be removed without losing the story’s overall intent, purpose, mood and core ideas.

Most importantly, film style and literary style are so fundamentally different that changes must be made for the transition from page to picture to work. Novels are a literary art form while films are a visual art form. Point of view in a novel is expressed through language, while in cinema it is expressed through cinematography, editing and sound. A novel must describe things like setting, costumes and the appearance of the characters, while a film has to show it. Novels can play with tense and reveal the inner thoughts of characters in a way film cannot. Film can incorporate music and use montage to create emotional associations in a way that is impossible in a print medium. Dialogue is used, or should be used, completely differently in novels and films. What a character says in a novel can be drenched in subtext and doesn’t have to always be written on the page word for word, while dialogue in cinema has a more functional purpose. On the other hand, film can use techniques such as visual and sound motifs, directional lighting, acting and camera effects such as focus pulls to suggest subtext and symbolism.

Films are supposed to adapt the source material, not directly replicate it or try to second guess what the majority of the audience expects to see based on their own subjective reading experience. Personally, I love the way a story and its characters can be transformed for the medium of film when a favourite novel of mine is adapted. Mark Romanek’s film adaptation of Kazuo Ishiguro’s novel Never Let Me Go conveyed the novel’s melancholic story of love, loss and fate far better by leaving some things out than it would have if the film directly reproduced key scenes. The extensive changes to style and structure in Lynne Ramsay’s film version of Lionel Shriver’s We Need to Talk about Kevin produced a work of extraordinary cinematic subjectivity in which sensory memories were visualised.

Sometimes, a film adaptation is a great work in its own right while also being extremely close to the source material. Steve Jacobs’ excellent adaptation of JM Coetzee’s novel Disgrace remained faithful to the novel, as did John Hillcoat’s adaptation of Cormac McCarthy’s The Road. Then again, to demonstrate that you never can win, some critics praised the film’s bleak cinematography for articulating a sense of McCarthy’s sparse prose, then complained that they therefore couldn’t see the point in the film being made in the first place since it was so similar.

Still, films like Disgrace and The Road are exceptions to the rule – in the end, they are great not because of their fidelity to the source material, but because they are excellent films. The value of a novel adaptation is primarily how well it works as a film, and to a lesser extent, how well it expresses the essence of the source material rather than how well it mimics it. The book is never better than the film; the two are incomparable. It’s not reasonable to critique a film for not functioning in the same way that a novel does. A film may fail on cinematic grounds, but it should not be accused of failing on literary grounds. Once literature-loving filmgoers accept the fundamental differences between novels and films, they can move beyond feelings of outrage whenever a film supposedly butchers, murders or destroys an esteemed novel, to become far more relaxed and open-minded when going to the cinema.

Thomas Caldwell is a Killings columnist, and a writer/broadcaster specialising in film criticism.