“Smallville” (8 p.m., The CW): Some major changes are in store for

“Smallville” (8 p.m., The CW): Some major changes are in store for “Smallville” as it launches Season 8. Actor Michael Rosenbaum has left the show, so say good-bye to Lex Luthor. Also, Clark Kent finally moves to Metropolis to take a job with the Daily Planet.

“Supernatural” (9 p.m., The CW): In the fourth-season opener of “Supernatural,” Dean is freed from a stint in Hell and he’s emerging with no memories of what went down in the Devil’s playground. Maybe that’s a good thing.

“Burn Notice” (10 p.m., USA Network): As the summer season draws to a close, Michael poses as a security adviser to foil a kidnapping plot.

“It’s Always Sunny in Philadelphia” (10 p.m., FX): Your first experience with “It’s Always Sunny in Philadelphia” is a little like when you had your first drink. You feel momentary breathlessness, maybe you cringe, you wonder can you finish what you’ve started. Then it gets easier to stick with. You might even realize you like it.

That’s the kick you can expect from FX’s overproof comedy, which returns for its fourth season with back-to-back episodes Thursday at 10 p.m. As usual, the action largely takes place at (appropriately) a rundown pub in Philadelphia co-managed with ineptitude by longtime chums Mac, Charlie and Dennis, as well as Dennis’ sister, Sweet Dee, and their father, Frank.

There’s something eternally conniving, self-absorbed and oblivious about each of these characters, who pursue the most outrageous schemes, never succeed and never learn.