For the ninth time this semester, the high-school senior from a Chicago suburb has faked an illness (licking his palms to make them clammy is his preferred "nonspecific symptom") to fool his dotty parents into letting him "ditch" school. Now, speaking directly to the camera, he says: "If I go for 10, I'm probably going to have to barf up a lung."

Ninety minutes later, the discerning movie- (note well: I do not say "film-" or "cinema-") goer leaves the theater saying: "At last, that is settled. Arguments can rage about whether the second greatest movie is this or that exploration of Scandinavian angst or this or that study of men in black turtleneck pullovers who suffer urban dread in Paris or Milan with women who drink bitter coffee and wear their hair in buns and ceramic earrings they crafted in their backyard kilns. But for those of us who seriously doubt that movies are often serious, it is clear that the greatest movie of all time is showing now at fine theaters everywhere.

It is "Ferris Bueller's Day Off." By "greatest movie" I mean the moviest movie, the one most true to the general spirit of movies, the spirit of effortless escapism.

Remember Steve McQueen in "The Great Escape," busting out of a German POW camp? Ferris "borrows" a friend's father's Ferrari and escapes for a day from something worse: high school. As should happen in a teen-ager liberationist movie, Ferris reduces a ferret-faced school administrator to rubble, bamboozles his soggy-headed parents and lives out every teen-ager's fantasy of subverting authority at every turn. Ferris is, as the saying goes, "into" fun. The movie will elicit cliche's -- what America's premier essayist, Joseph Epstein, calls "ephemeral verities." The cliche's will be to the effect that Ferris is a symptom.

Need you ask of what? Of the self-absorption of youth corrupted by the complacency of the Reagan years. Such Zeitgeist-mongering is punctured by Epstein's question: When, other than periods of war or economic calamity, have people not been self-absorbed?

"Ferris Bueller" is -- let us blurt out the worst -- not serious. But, then, few movies are, and fewer should be. Here is an oddity of our age. Many people would rather undergo torture or (what is much the same thing) have a Judith Krantz novel read aloud to them than have it said that they willingly read third-rate novels, yet those people go to movies that are the moral equivalents of Krantz novels, and will read ponderous reviews of those movies. Epstein, who believes that much movie reviewing amounts to distinguishing between the fourth-rate and the third-rate, says that reading Pauline Kael, "page after page, on, say, the movie 'Popeye' becomes a spectacle akin to listening to someone play 'Mares Eat Oats and Does Eat Oats" on a Stradivarius."

h, carry me back to olden days, when almost all movies were like "Ferris Bueller" -- no nonsense about seriousness. In the early 1950s, the 11-year-old intelligentsia in Champaign, Ill., plunked down 10 cents for a double feature plus a "festival" of five cartoons, and for another five cents they could pig out on Jujyfruits. (Today's younger generation, like every younger generation, is dismaying, but has minted a magnificent verb: "pig out.") Alas, in the 1950 movies became "films" and seriousness settled like soot over everything.

"Universities," Epstein recalls, "had film societies, and every major city had at least one little art house, where a pallid young woman smoking a Russian cigarette looked up contemptuously from her Baudelaire long enough to sell you a ticket for a Peruvian film that opened on a scene of peasant boys slaughtering a vicuna." The fruits of such seriousness were, and are, enough to make you sympathize with the movie-goer who left a theater exclaiming, "I don't ever want to see a movie I haven't already seen before."

Make an exception for the sage of Ferris Bueller, whose credo, like that of every red-blooded teen-ager, is "You can't go too far." But be braced for this fact: Teen-agers go too far with bad language.

It is, perhaps, best to shrug and say, as a critic did, that vulgarity is the garlic in the salad of life. Besides, before you wince and writhe and fear for the republic because of the coarseness of the children, remember the kind of vulgarity you hear on news broadcasts, from journalists who ask questions such as (Epstein's examples), "What did you think when you first heard your husband had been killed?" or "What went on in your mind when you learned that you had cancer, now for the third time?" or "Tell me, Holy Father, have you never regretted not having children of your own?"

Ferris and his friends have their faults, including a weakness for bad words, but at least they do not talk like that.