Technological Advancement
The plot of the movie revolves around the introduction of sound to movies and how the rush to completely transform an industry outpaced the medium itself. Entire careers were suddenly brought to an end when the silent movies starting talking, as the requirements of "talkies" were entirely different from the requirements of silent films. The film makes comedic hay out of this impact on careers through the story of Lina Lamont's gross incapabilities as a talker. Singin' in the Rain takes a satirical approach to an enormous shift in the entertainment industry, which makes way for the invention and development of the movie musical—the genre of Singin' in the Rain itself. Film is a unique industry in that artistic developments have been directly connected to technological ones, and Singin' in the Rain demonstrates this.
Illusion vs. Reality
A major theme of the film is that pretty much all of show business is based on illusion. When we first meet Lockwood at the premiere for The Royal Rascal, he has crafted a backstory for himself that is entirely at odds with the reality that is revealed to us in a montage. Lina’s voice has to be dubbed because it doesn’t align with her image as great romantic lead. The Cyd Charisse fantasy sequence is framed through an acknowledgement that movies are all light and shadow, pleasing viewers and distracting them from the illusion so that they can believe, momentarily, that it is real.
The interplay between fantasy and reality becomes very important to the story. That which seems real is often fake, but the shared illusions of fiction can also add up to authentic experience and emotion. The clumsy interplay between illusion and reality is perhaps most starkly on display in "Make 'Em Laugh." Cosmo manages to pull off a pretty athletic move by running up a wall and doing a backflip not once, but twice. When he attempts a third time, however, he has mistaken a flimsy set backdrop for a real wall and goes flying right through it.
Romantic Love
The soul of the film is the love shared by Lockwood and Kathy. Their love is authentic and real, in contrast with the illusory, manufactured love affair that the public has imagined exists between Lockwood and Lina. For the sake of their careers, Lockwood must pretend that he cares for Lina, and Lina believes in the illusion for the good of her own career.
When Kathy enters Lockwood's life, the emotions he starts feeling toward her become so overpowering that he becomes enamored by her discerning and honest personality. He falls almost instantly in love with her, in spite of their bumpy start, and expresses his love for her earnestly and with a musical flair. The couple become inseparable and enduringly supportive. At the end, not only does Lockwood expose that Lina's performance is a sham, but he also exposes his previously hidden relationship with Kathy, and shows the world that they are in love, catapulting them both to fame and glory.
Fame
Speaking of fame and glory, fame is a major theme in the film. After all, the setting of the film is Hollywood in the 1920s, and the central characters are the two biggest stars of the silent film era. When we meet Don Lockwood, we see that fame elevates him and gives him a lot of power, but it is also alienating, forcing him into a relationship he doesn't want to be in, and sometimes it even ruins his jacket. When he gets out of a car downtown with Cosmo, he is accosted by adoring fans who rip his jacket and send him running.
Singin' in the Rain portrays fame as a double-edged sword. Both the costs and benefits of fame can best be summarized in Cosmo's quote, "The price of fame. You've got the glory, you gotta take the little heartaches that go with it. Now look at me: I've got no fame, I've got no glory, I've got no big mansions, I've got no money! But I've got—what have I got?" Fame is both enviable and a headache, but ultimately, the movie suggests, it's worth it.
Cinema
Clearly, a major theme of Singin' in the Rain is the movie business, as Lockwood is a major film star and much of the film is set on a Hollywood soundstage. Throughout, we see the ins and outs of the movie business, a perspective which at once elevates and demystifies the world of film. On the one hand, we see how illusory so much of the movie business is, and on the other, we realize that these illusions create some beautiful, moments—not only for the audience, but for the performers themselves. When Kathy first meets Lockwood, she looks down at the movie business and its "undignified" nature, sneering at the fact that the people in movies are only "shadows," while actors in the theater are living, breathing human beings. She soon changes her tune, however, when opportunity starts to knock in Hollywood. Hollywood is portrayed as a tough town to break in to, a ruthless industry in which everyone's trying to get ahead and the odds are always against you. It's also satirized affectionately as just another business, albeit a less stable one, with egos, talent, pitfalls, and magic galore.
The Show Must Go On
Part of what makes Singin' in the Rain so charming is the fact that it is so persistently optimistic. No one's troubles last very long in the film, and this is partially just the tone of the film, but it can also be attributed to the plucky, resilient, and positive attitude of the characters. When Lockwood is depressed about not knowing where Kathy Selden is, after having run into her at the party at Simpson's, Cosmo urges him to look to the wisdom of show business and remember that "the show must go on." This saying means that no matter what goes wrong, it is important to keep going and try to find opportunities where one can, to see the silver lining and move forward. Throughout, we see this philosophy inspiring numerous characters. When The Dueling Cavalier fails, Cosmo comes up with the idea to turn it into a musical. Lockwood and Kathy think this is a great idea: they are reinvigorated, and they dance triumphantly, singing "Good Morning." With enough optimism and the ability to pick up the pieces and move on from failure, the characters are able to create happiness for themselves.
Imagination
Part of what allows the characters to move forward and be so resilient in the face of setbacks is their well-developed imaginations—their ability to make something out of nothing. We first see the imagination at work in the beginning, when Lockwood describes his upbringing; his description is markedly higher brow than the reality that we see in montage. By manipulating the truth and using his imagination, he is able to create a more glamorous autobiography for himself.
The next instance of imagination being a major theme in the film is when Lockwood professes his love to Kathy. Before he can tell her he loves her, he says, "I’m trying to say something to you, but I’m such a ham, I guess I’m not able to without the proper setting.” That "proper setting" is an empty soundstage. On it, he changes the lighting scheme, switches on a large industrial fan to create an "evening breeze," escorts her onto a ladder and tells her that she is a woman standing on her balcony overlooking a garden. He uses the illusory technologies of cinema to invite Kathy into a fantasy, to use her imagination with him. Only then can he tell her how he feels.
Additionally, the entire "Broadway Melody" sequence is a figment of Lockwood's imagination. As he begins to describe his vision to Simpson, the viewer is transported into it, and we see the entire number unfold with elaborate costumes and dance sequences. When it ends, we realize that it was all a figment, that we are still in Simpson's screening room, and Lockwood is simply making a pitch. In his imagination, however, the number is fully formed and breathtaking, an immense spectacle.
