One of the many reasons to watch the first three seasons of “Community,” the fiercely quirky and unapologetically smart NBC sitcom, was that you actually had to watch it. Every offhand remark, every reaction shot, every bit of physical business communicated something (usually something funny). More than any other show in prime time it demanded that you pay attention.

The sad simulacrum of “Community” that checks in Thursday for Season 4 makes no such claim on your concentration. Send a few e-mails, look at the television, order a pizza, look back at the TV. You won’t miss anything important, because there’s nothing important to miss.

Dan Harmon, the man who created “Community” and its misfit collection of community-college study partners, was cut loose after last season, a victim of low ratings — the series averaged four million viewers and finished 144th among prime-time shows — and of having a reputation for being difficult to work with. Rather than cancel the show, which finished a more encouraging 102nd in the crucial 18-to-49 demographic, NBC handed it to a new pair of producers, David Guarascio and Moses Port. Replacing an original show runner has been in vogue lately, and it’s not by definition a bad thing. “The Walking Dead” did fine when Frank Darabont was replaced by Glen Mazzara (who has since been replaced as well), and the jury is still out on “Smash” after Theresa Rebeck’s departure. But with “Community” the drop-off looks startling.