One features family members who haven't aged since the show began and storylines that skew reality into a densely colored, animated landscape.

One features family members who haven't aged since the show began and storylines that skew reality into a densely colored, animated landscape.

The other has been built around an ever-changing cast of characters with plots "ripped from the headlines" and outcomes played out in many shades of gray.

"The Simpsons" and "Law & Order" are two of the three longest-running primetime series in network history and, as they begin their 21st and 20th seasons this weekend, they stand as twin pillars of the evolution of television. Both are constantly in repeats, both re-energized their genres and both are the seeds from which other franchises have grown.

"Family Guy" was nominated for an Emmy as Best Comedy Series this year, but its success (and that of shows such as "South Park," "King of the Hill," "Futurama" and "Robot Chicken") would never have happened without "The Simpsons" breaking the bias against primetime animated comedies.

But "The Simpsons" has done more than open the doors for animation and special effects. There has been a freedom in its depiction of the family dynamic that has influenced real-life sitcoms, and the rhythms of its writing can be heard in shows that followed such as "Malcolm in the Middle," "Boston Legal" and, currently, "The Big Bang Theory."

In the years leading up to "Law & Order," police and courtroom dramas had degenerated from the gritty realism of early television to shows dependent on quirky detectives, lawyers and private eyes — with only an occasional "Hill Street Blues," "Rockford Files" or "Cagney & Lacey" thrown into the mix.

"L&O" changed that, replacing the emphasis on star-power with a focus on storylines. Plots weren't drawn in a straight line; trial outcomes could frustrate the viewers as much as the district attorney's office.

The crime procedural returned, and became the gensis of "franchise" television. There are three "L&O" shows on the air this season, along with three "CSI" shows and two under the "NCIS" brand. If it returns for a 21st season, "Law & Order" will surpass "Gunsmoke" and become the longest-running drama in television history.

At 8 p.m. Friday, NBC airs the 444th episode of "Law & Order." At 8 p.m., Sunday, Fox shows the 443th episode of "The Simpsons."

Friday, Sept. 25

One of the odd trends of television is its obsession with being able to commincate with the dead. You'd think the dearly departed might have better things to do, but apparently even mortality doesn't release you from the angst of not finishing everything there was to do on Earth. "Ghost Whisperer" and "Medium" return for a two-hour block beginning at 8 p.m. on CBS, ready to ease poor souls not quite ready to leave.

Saturday, Sept. 26

On the subject of shows that have been on forever, "Saturday Night Live" returns for season No. 33 at 11:30 p.m. on NBC. Actress Meagan Fox (who was born four years after John Belushi died) is the guest host, with U2 providing the musical interludes between sporadically funny set-pieces.

Sunday, Sept. 27

"The Wizard of Oz" turns 70 this year and, in case you were lucky enough to score tickets to the special screening at Tinseltown, TBS is running the classic at 8 p.m. Long before kids decided who was their favorite Beatle or character in "Gossip Girl," we were deciding whether we were a Scarecrow, Tin Man or Cowardly Lion. (I'm not telling.) Fans of intelligent and fun kids' films are in luck, by the way; "Oz" is followed by a more recent standard, the Astoria-filmed adventure "The Goonies."

Monday, Sept. 28

Charm and wit go a long way when you are being asked to bring characters into your home each week. One fairly new series that has those qualities in great supply is "Castle" (10 p.m., ABC), which follows a mystery writer who alternately teams up and annoys the police detective on whom he's basing his newest character. Nathan Fillion, as the writer, and Stana Katic have a good chemistry working here.

Tuesday, Sept. 29

I'm going to use this moment to talk about a show I can't stand. "Hell's Kitchen" is a well-produced exercise in sado-masochism masquerading as a cooking competition. The contestants are berated by head chef Gordon Ramsey. The lucky ones get eliminated; the season's "winner" gets, as their prize, the chance to ... CONTINUE WORKING FOR THIS MANIAC! At a time when getting (and keeping) a job is a dicey proposition, this is one kitchen that should be closed.

Wednesday, Sept. 30

I've held off talking about "Glee" (9 p.m., Fox) because I wanted to be sure that the musical format would maintain the standard of this spring's stunning pilot episode. It has. This week, the high school glee club gets some help in the form of a ringer — a former member played by the always-watchable Kristin Chenoweth. If a high school-oriented show about a mismatched singing group seems out of your comfort zone, consider that "Glee" is as universal in its themes as that show about mismatched high school kids who slayed vampires.

Thursday, Oct. 1

There are far worse ways to spend a half-hour than watching "It's Always Sunny In Philadelphia." A two-hour block begins at 10 p.m. on FX and, since it's a comedy that runs that late a night, you probably shouldn't expect to see something for the kids. "Sunny" has an edge and isn't always for everyone's taste; but if you like your humor with a touch of snark (and a heaping helping of Danny Devito), then you might give it a try. You could do worse ... you could watch "Hell's Kitchen."

Mail Tribune news editor Robert Galvin writes about television for TV Tempo. He can be reached at rgalvin@mailtribune.com