With Johnny Carson retired from ''The Tonight Show,'' leaving us to Leno, Letterman and the rest, we watchers of late-night talk shows are experiencing a change in style -- from classical to post-modern.
Mr. Carson's show was classical in that it offered a transparent window on his guests' various talents. David Letterman's show is post-modern in that the medium is partially opaque. Mr. Carson's cameras stayed invisible, politely focused on the set and the guests. Mr. Letterman jostles ''our'' camera at some point in nearly every opening monologue. He throws pencils at us. Why? To acknowledge the artifice, to be un-phony by displaying the phoniness.
Mr. Carson always gave a genuine comic monologue. Set-up and punch, set-up and punch, weaving together today's headlines with items of sheer mirth.
Exit the mirth of a nation, enter the derision. After Johnny's classical period, talk-show decadence now has its day. Mr. Letterman's half-hearted pretense at a monologue is itself a kind of joke. Even supposedly hip cynicism grows depressing after a while. Yet Johnny's show seemed to exult, perhaps more innocently than is now the fashion, in the value of life. That's probably what we'll miss the most.
Johnny's classicism may seem old-fashioned next to his successor at NBC, Jay Leno, whose snack-food ads run on MTV. But Mr. Leno is less hip than Mr. Letterman. In terms of style, there's a continuum: Johnny was the classic, Mr. Leno and Arsenio Hall are modern, and Dennis Miller and Mr. Letterman are post-modern. The scale refers to the relative transparency of the medium itself.
Mr. Miller, for instance, is the only one now making a regular prop of the studio monitor's applause sign. There and elsewhere in his new show, he adds a new kind of humor, that of text appearing on the screen, which is obviously an up-to-date style of our
Mr. Letterman's ''Top Ten List,'' when you think of it, is a kind of computer-screen scroll unfurling its punchlines. But let's not mistake the post-moderns' use of superimposed text as some fresh wave of intellectualism sweeping the tube: On all these late-night shows (including ''Saturday Night Live''), the hosts are still careful to read to us the text that appears on our screen.
Johnny's shows almost always were videotaped in one take, in ''as-if-real'' time. His producers took the show's classical unities of time and space very seriously. You could watch the show as if it were all just happening as you watched.
The newer shows, though, present themselves as things that could happen only on video. With the cameras jerking around ''Late Night Thrill-cam'' style, and the (''Hal, roll that tape'') endemic use of videotape, post-modern TV treats time and space as stuff waiting to be spliced and diced. These newer programs, conceived since the cable explosion, have been designed to simulate channel ''zapping.'' Mr. Letterman, most notably, with his out-of-the-studio tape packages, overtly acknowledges that his show's reality is not the virtuosity of as-if-live, but rather as if (because it really is) on tape.
The good side to post-modern TV's self-consciousness is that it can seem more honest, less deceptive about its illusions. The down side is that the self-consciousness leads to narcissism.
TV as a medium has developed a bad habit, recently, of casting its own shadow over the picture. We saw it in the coverage of the gulf war, and we see it in the producers, cameramen and stagehands who play sullen on-camera characters on ''Letterman.'' Here again, Johnny kept the screen clear for us. Mr. Letterman's show, like much of MTV, is largely about being on TV.
But if there is a change of style between Johnny and his successors, the function of these shows, no matter who hosts them, remains the same. Their very profusion, and the impressive ratings they get, suggest that whether classical, modern or postmodern, light entertainment with celebrities talking about themselves is what Americans prefer to watch at that hour. Stay up late and hear some jokes, marvel at some tricks, see the stars come out.
These shows perform a liturgical purpose at the end of the weekday: amusing us, reassuring us and preparing us for sleep. Styles may come and go, but the tube has learned at least to do that. Thanks, Johnny, for sending us to bed smiling.
Brian Stonehill, who teaches at Pomona College, is completing ''What to Watch For,'' a handbook of visual literacy. He wrote this commentary for the Christian Science Monitor.