In answering the titular question, I will begin with this opinion; what makes each art form great is that which makes it singular.
What makes music great is its ability to convey an emotional journey through patterned lyrics and melodies. What makes literature great is its ability to conjure up a universe using well-chosen words. What makes visual art great is the manner in which it captures events through purely optical means.
Within the motion picture, sight, sound and word band together in pursuit of an emotion or idea.
Of course, live theater also features this threefold combination, with a spontaneity and immediacy that the cinema does not possess. So, what exactly is cinema capable of that the theatre is not?
It is capable of extremes.
An example from the repertoire of the Lumiere Brothers, the worldâ€™s oldest major filmmakers, will provide sufficient evidence of this point. Their first release, the riveting â€œWorkers Leaving the Lumiere Factory,â€ is a 45 second shot of a crowd of tired wage earners leaving their day job.
This sequence, with its hundreds of men and women spilling out into city streets, would be nigh impossible to stage in an orderly or visually appealing manner. But, in film, the location of the camera alleviates this problem. By stationing said camera far away from the factory doors, the filmmakers capture an image too large for the stage.
There are also, it turns out, images too small for the stage, images that may be captured in what is perhaps cinemaâ€™s greatest artistic contribution, the close-upâ€” the only existing way in all of art for us to see the moving, thinking, reacting human face at minimal distance. I think of â€œSophieâ€™s Choice,â€ where Meryl Streep has to choose which one of her children to save. Only the closeness of the movie camera can convey the multitude of emotions flashing across her face in quick, terrifying succession.
On a lighter note, only the movie camera can convey the look of sheer horror on Woody Allenâ€™s face in Annie Hall, when a crazed Christopher Walken (is there any other kind?) is driving him to the airport.
The other thing that makes movies great is embedded in their very name: they are capable of moving, and of using that movement to make statements.
Take the deservedly famous opening of â€œThe Godfather.â€ It begins with a close-up of a man speaking directly to us. He sounds confident and authoritative. However, as the scene progresses, it becomes clear that he is not giving a speech, but instead asking a favor of a mob boss. As his declaration turns into a plea, the camera slowly moves away from him, until he is finally seen, small and distant, over the mobsterâ€™s shoulder.
Working in tandem with words and sounds, the camera reduces the speaker from powerful to powerless in a matter of seconds.
When movies accomplish feats like this, when they enlarge our ways of seeing and being by making great and innovative use of scope and motion, they do more than bring us joy. They justify their own existence.