A convincing fan theory can explain why Community’s study group always left a chair free at their table. Dan Harmon’s meta sitcom ran for six seasons (and, so far, no movie). While Community's cast chopped and changed in later years, the study group possessed one constant feature throughout the show’s duration. Their table always had an empty seat. One theory for the existence of the empty seat has become particularly popular with fans.
Community was successful due to its compelling host of characters and witty writing. However, the show stood out amongst other sitcoms of the era because of its meta-narrative and self-parodying. Abed Nadir, creator Dan Harmon’s mouthpiece in the show, was constantly on the verge of breaking the fourth wall. Though Danny Pudi's character certainly seemed to have a different perception of his surroundings, it's still unclear if Abed knew he existed in a TV show.
This is why many fans believe that the mystery of the free chair was Dan Harmon’s greatest meta Easter egg in Community. The core study group, which led the show during its more successful early seasons, had seven members: Troy, Abed, Britta, Annie, Pierce, Shirley, and Jeff. So, why was there an eighth chair at their table? A popular Community fan theory (via Reddit) suggests that the final seat at the study group’s table was left empty for the audience. This remains popular because, if true, it would serve as the ultimate meta element of Dan Harmon's show. If the audience possessed a literal designated seat at the table, the barrier between viewer and Community would crumble.
The theory’s primary defense is that it fits with Community’s unique style and identity. The show was frequently self-referencing, and Abed appeared to understand he was in a TV show. Therefore, to learn that the audience was an invisible member of the study group would not be surprising. Furthermore, Dan Harmon was known for being interactive with fan comments, discussions, and criticism during his tenure as Community head writer. So, to give fans clear recognition in his story would be very on-brand for the series creator.
Offering more support to the theory, in the same Reddit thread, it is mentioned that marketing companies often leave chairs free in table scenes so that customers feel invited to join in. If advertisers have used this technique to welcome customers, it would be cleverly fitting for the TV writers and directors to do the same. Perhaps, showrunner Dan Harmon felt that, by leaving a seat free at the study group’s table, he could make the audience feel more connected to the characters and the show.
Granted, there are some counter theories that are somewhat convincing when it comes to the empty chair in Community. Offering an alternative idea, the Reddit thread countered that the empty chair could have been left for Jeff’s enormous ego. Other fans have wondered whether the chair might have been reserved for special guest stars. However, the study group table having a seat free for the audience is the most Community-appropriate answer to the mystery. Dan Harmon’s show was very deliberate, and his writing was very detailed. It seems unlikely that such a clearly visible Easter egg would not have been carefully planned by the Community creator.