A book I was reading a while back referred offhandedly to Frank Baum's conception of Oz as a dream. The writer must not have read Baum's book, where Dorothy's journey to Oz is never suggested to be a dream. That idea came from the 1939 film. It's striking that so many people remember The Wonderful Wizard of Oz, one of the most beloved stories of the twentieth century, through the famously interpretive screen adaptation.
Ironically, Baum disliked the "it was all a dream" convention in literature. (He must have turned in his grave in 1939.) I agree with him. It's a much overused device that has the smell of copout. I can understand its use in Alice in Wonderland, which deals with absurdity. But Oz, beyond being magical and impossible, is hardly absurd. Dorothy's adventures seem far too coherent to plausibly represent a dream. Therefore, why did the 1939 film work so well?
My theory is that it worked by largely ignoring the dream motif. Sure, it linked several characters in Oz to people Dorothy knew back in Kansas, none of them from the book. But once the movie reached Oz, it portrayed the book's events more or less faithfully.
Had the movie been made today, I don't think they'd have gotten it right. Modern movies--from the 1970s onward--are much more naturalistic than old ones. It's a prime reason for the decline of musicals. In recent musicals like Dreamgirls, there's a certain awkward, pretentious quality that didn't exist back in the 1930s, when audiences found nothing strange about seeing characters burst into song. That kind of casual surrealism doesn't jibe with the style of modern movies, which aim to evoke a feeling of reality. Acting is more understated, scenes more slow-paced. In this climate, movies about dreams try to approximate what dreams actually feel like, which is to say, fleeting and bizarre. This approach limits the possibilities in some ways while broadening them in others.
Many sitcoms have featured at least one episode in which a character is dreaming. The classic example is the "Twilo" episode of Dick Van Dyke, where Rob dreams of going to work and discovering that all his friends have turned into pod people, in a hilarious sendup of Invasion of the Body Snatchers.
But what works in a twenty-minute sitcom doesn't necessarily work in a feature-length film. The conceit of having a story take place almost entirely in a character's head has inspired some dreadful films. Two that come to mind are Give My Regards to Broad Street (1984) and Delirious (1991). The first is more or less an extended music video by Paul McCartney. The second is a spoof in which John Candy plays a soap writer who dreams he finds himself trapped inside a real-life version of his own show. In both films, the story becomes increasingly jumbled as it progresses, and the protagonist wakes up before he completes his mission. That's just what dreams are like, but what fun is there in watching a movie with those qualities?
The problem with using dreams as a basis for comedy is that comedy requires rules, and dreams have no rules. You can get a quick laugh out of the absurdity of a dream, but dwell too long on the conceit and it starts to become more strange than funny.
Nowadays, the more ambitious films about dreams tend to embrace the weird factor. Three that come to mind are the Spanish thriller Open Your Eyes (remade in the U.S. as Vanilla Sky), the David Lynch drama Mulholland Drive, and Richard Linklater's Waking Life. In all these films, we're led to suspect that a significant amount of what we see is a character's dream, but the extent of it is left tantalizingly ambiguous. These films greatly exploit the old philosophical conundrum that it's impossible to know for sure at any moment in our lives whether we're dreaming or not.
Exploring that kind of dilemma would have tanked The Wizard of Oz. Unlike modern movies on dreams, it retained a straightforward approach to the storytelling. Because it wasn't bound by the belief that a movie about dreaming must display dreamlike qualities, it didn't try to alter the story to fit a preconceived idea of what dreams are like. This kept the essence of the story intact even as the dream motif gave the story an added psychological dimension, a balancing act that today's movies have forgotten how to achieve.