Walking away from the camera, down a dirt road, his cane bobbing behind him, Charlie Chaplin is not a comedian but a clown. Emmett Kelly was the same kind of clown, smiling through a painted-on frown.
In Chaplin's films, the frown is painted on with a camera, and the audiences have to supply the smile themselves. Chaplin's deadly seriousness makes it clear that he does not understand why the joke should be on him….
The difference between Chaplin and the other great screen comics was that Chaplin played a clown. The others, by and large, played comedians, with a few exceptions such as Lahr, Keaton, and possibly Jerry Lewis.
Comedians and clowns aim in opposite directions. Comedians live in imaginary worlds that look just like our own. In "The Apartment", for example, Jack Lemmon inhabited a flat as realistic as it was unlikely.
Clowns, on the other hand, live in real worlds which consist of a few props. No worlds are more real than the clown-worlds of "Waiting for Godot" or Chaplin's early shorts.
Comedians use fantasy to make the real world seem funny. Clowns use reality to make our fantasies seem ridiculous.
Chaplin was also the only one in his world who believed in its conventional morality. He believed honor should be defended. He believed customers in restaurants should be polite. He believed little flower girls, especially if they are beautiful and virtuous, will be treated kindly by the world. In short, he was naïve.
It's almost as if everyone in Chaplin's world was a W. C. Fields, and everyone in Fields's world was a Chaplin. Fields took great relish in beating down the naïve idealists ("Out of my way, you fools," he once snarled at a flock of chickens). But Chaplin never did quite learn how to handle the cynics. And that was the point of his art.
Roger Ebert, "Of Comedians, Clowns and the Cinema," in The Chicago Sun-Times (reprinted with permission of Chicago Sun-Times), March 26, 1967.