It has become a bittersweet ritual of spring. Every year, the end of the TV season means the final episode of a long-running show and fans saying goodbye forever to favorite characters. Every few years, though, the experience becomes deeper and often downright painful, as fans say goodbye to landmark shows and characters they have connected with in profound ways. In the 1970s, there was Mary Richards turning out the lights in the newsroom at WJM-TV in Minneapolis, and the Stivics going off to California, leaving Edith and Archie behind. In the 1980s, a psychically wounded Hawkeye Pierce came home from Korea, and a bushy-tailed Alex P. Keaton left home in search of his fortune. Thursday night at 8 on NBC, the most popular show of the 1980s and the most watched show in the history of TV ends its eight-year run, as the Huxtables gather in their townhouse for the college graduation of Theo in a final episode of "The Cosby Show" titled "Together We Commence." There is not much talk today of "Cosby" parties, like the "M*A*S*H" parties when that show ended with the largest audience ever for a regular series at that time. Nor is Bill Cosby's face on the cover of every magazine at the newsstand, as Mary Tyler Moore's was when Mary Richards said goodbye. But there are reasons for that -- reasons that have more to do with some of us in the audience than with the show. "The Cosby Show" is every bit and then some as culturally significant as "M*A*S*H" or "The Mary Tyler Moore Show." It's landmark TV by any yardstick you choose. Improving race relations Because it was the most watched show of all time, it made more money than any show -- both in its first run on NBC and in its syndication to stations, like WJZ-TV (Channel 13) in Baltimore. Because it was the most popular show of the '80s, it has valuable things to tell us about that decade -- things that &L; challenge conventional wisdom. But most important, say media critics and historians, "The Cosby Show" changed racial attitudes for the better like no single TV show ever: It helped make the 1960s' rhetoric of "black is beautiful" an emotional and spiritual reality for many viewers of many different races. And that's a lot for a seemingly simple, little, family sitcom that some critics condescendingly referred to as "nothing more than a black 'Father Knows Best.' " J. Fred MacDonald, author of "Blacks and White TV: African Americans in Television Since 1948," says that "The Cosby Show" accomplished so much that many of its victories are overlooked. "Take the show 'Cheers,' with everybody lauding it today as a great show," says MacDonald, who teaches history of broadcasting at Northeastern Illinois University. "It was 'Cosby' that made it a hit show. 'Cheers' foundered for the first two years until they put 'The Cosby Show' in front of it by half an hour. It was 'The Cosby Show' followed by 'Family Ties' with Michael J. Fox, and then 'Cheers.' "Right after NBC set that lineup, 'Family Ties' shot up in the ratings, and 'Cheers' shot up in the ratings -- all because of Cosby. Before that, the highest 'Cheers' ever did was 32nd." And, that move in 1985 led to NBC dominating Thursday nights. And the domination of Thursday nights led to NBC becoming the first place network straight through the 1980s and into this season, when CBS bumped it off two weeks ago. By the end of 1987, industry analysts said it was impossible to calculate how many hundreds of millions of advertising dollars across the schedule the "The Cosby Show" had already meant to NBC. MacDonald also points out that the instant and phenomenal success of the show "sparked a renaissance of the sitcom genre" -- with a flock of similar family comedies, like "Growing Pains" and "Roseanne," springing up in its wake. But, like everyone contacted for this story, MacDonald said the show's greatest contribution was in the cultural impact of its presentation of images of African-Americans. Positive images "The series demonstrated that successful programs need not recapitulate racist notions of how African-Americans acted, nor limit the number of blacks on screen in order to sustain the myth that significant American life was lily white," MacDonald said. "For the first time, network TV offered a black nuclear family that was believeably human -- where parents nurtured their children, and children loved their mother and father and related with each other respectfully; where audiences laughed with the wittiness, not at the pejorative tomfoolery, of its leading characters. . . . And it did all that in a recognizable situation of the sitcom that viewers were comfortable with." The progressive message on race presented in the conservative wrapping of the traditional sitcom is one of the keys to appreciating the show, according to Lawrence Mintz, who teaches popular culture and humor at the University of Maryland in College Park. "Probably the most significant thing about the Cosby show is what was the same and what was changed," Mintz says. "In a very dramatic way, it had the traditional sitcom structure -- so much so that it was seen as neo-conservative. . . . But because that structure was so pronounced, some people didn't notice at first what was so very different about the program: It had black heroes and heroines, . . . positive role models. "That strikes me as very important -- that the majority of Americans were apparently willing to accept . . . the black heroes and heroines, because of the familiar setting." A black 'Father Knows Best' A number of critics were unable to get past the traditional trappings to see the more radical message and appreciate how that setting brought the message to a wider audience. Because Cosby's Dr. Heathcliff (Cliff) Huxtable, M.D., wore a sweater and was an authority figure, the show was simply "a black 'Father Knows Best' " to them. It needs to be noted that such analysis came from white critics; there are only a few black critics working in the popular press. And it is not unusual for the dominant culture to try to minimize -- consciously or unconsciously -- the accomplishments of minority groups by casting them in such terms. Some male film critics did the same thing last summer when they described "Thelma & Louise" as nothing more than a "female buddy film." Furthermore, MacDonald says, "even if it were only a black 'Father Knows Best,' there's nothing wrong with that. The fact that in structure it is a black 'Father Knows Best,' but that its message was so radical, is an indictment of the networks and their . . . malignant neglect of racial minorities." There have been other criticisms of the show -- most notably the affluence of the Huxtables. But both Mintz and MacDonald also question that and where it's coming from. Cliff Huxtable is an obstetrician; Clair Huxtable is a lawyer. Their standard of living on the show is modest in terms of what such a couple could expect to earn, Mintz says. MacDonald calls their lifestyle "middle class" and adds that "there are many African-Americans who fit that category." Which is not to say that "The Cosby Show" is perfect on matters of race and what it accomplishes culturally. Critics say the Huxtables are not representative of most African-Americans and that "The Cosby Show" does not challenge the more fundamental aspects of racism in American life, and they are mainly right. As Michael R. Real says in "Super Media: A Cultural Studies Approach," the show "fails to address directly class and group conflict within American society." But, again, it's only a TV show. Let's not expect it to correct more than 200 years of racism in 22 half-hours a year for eight years. And, as Real also points out, "The Cosby Show" triumphs in "effectively countering generations of negative stereotypes of black males in family life" and replacing it with the positive image of Dr. Cliff Huxtable. Celebrating success The show's success is not limited just to Dr. Huxtable, either. From Frank Robinson to Stevie Wonder, Martin Luther King Jr. to Frederick Douglass, the show has consciously celebrated the accomplishments of African-Americans during its run. The message always seemed to be as important as the laughter to Cosby, who earned a doctorate in education from the University of Massachusetts with a dissertation on TV as a teaching tool. Remember when NBC wanted Cosby to remove an anti-apartheid poster from the wall in one of the kids' bedrooms because the network thought it might hurt sales of the show in South Africa? Remember Cosby's refusal? And, always, the emphasis was on higher education, whether it came from characters wearing sweat shirts from Tuskegee and Temple or the pride by Cliff and Clair in their childrens' success at Princeton and the mythical Hillman College. It's hard to imagine that the Huxtables won't be there anymore Thursday nights at 8 after Theo's graduation this week. But "Together We Commence" at least promises apt closure. Through a decade of divisiveness, Cosby has been teaching a message that can bring us closer together. The question is whether we learned enough to graduate into that multicultural, global future.