So, something else that I didn’t have room to talk about in my previous post on serialized TV: the distinction between serial and episodic is of course a bit artificial nowadays, since basically all dramas are serials by traditional standards. (Almost every show has some kind of ongoing story for the characters, even if those stories are kept way in the background and only mentioned occasionally, like the characters’ personal lives on Law and Order. What you don’t have, for the most part, is the old format where the weekly drama is really an anthology show with continuing characters, and no stories are carried from one episode to the next.) But there are degrees of serialization: some shows are hyper-serialized like Lost, some shows are a mix of serial and episodic like Chuck, while others are pure episodic shows with little bits of continuity.
There are several ways to gauge just how serialized a show is, but one method I particularly like is to ask the question: “Can this show do two-parters?” The two-parter is, almost by definition, a concept that belongs to the episodic format. Soap operas (the purest serials) cannot do two-parters because they don’t have individualized episodes (or, in many cases, even individual episode titles). A very serialized show can’t do a true two-parter because that implies that once the two episodes are over, a complete story has been told. Lost sometimes designates episodes as two-parters (Update: see Myles’s comment for more about that), but we’d never really know it if we didn’t know the episode titles. Since the stories in a serial all continue for several episodes at a minimum, it would be silly to call, say, last night’s Sons of Anarchy season finale “part 2” of the previous episode; every episode is a continuation of the last one to some extent. (Update 2: Jason Mittell, in comments, arguest that the Lost 2 parters are designated that way for a reason, and that the episodes have more individual identity than I’m giving them credit for.)
As Jerry Seinfeld pointed out, when you’re watching a show, you can “sense the To Be Continued coming” when you realize there are five minutes left in the hour, and they don’t have enough time left to end the story (“Timmy’s still stuck in the cave! There’s no way they can wrap this up in five minutes!”). Serials don’t normally have To Be Continued signs, because we watch them knowing in advance that the story will not be wrapped up at the end of the hour. The episodes are structured like Part Ones where Part Two never comes. This can have a negative effect on structure and individual episode identity, but it can also have a positive effect by freeing the episodes of the sense of let-down that often comes with the wrap-up section: the resolution, and the relaxation of pressure that follows it, are often the weakest moments of a stand-alone episode. The writer of a serialized show is free to end the episode at whatever point seems most exciting or interesting; what they lose in structural logic, they arguably gain in avoiding that inevitable resolution let-down.
So one way you can judge whether a show has crossed over from being an episodic show with serial elements, to being a serial with some stories-of-the-week, is whether the show ever does true two-part episodes, a double-length episode that clearly stands apart from the episodes that precede and follow them. Buffy The Vampire Slayer is one of the most obvious test cases. In its early seasons, it had some genuine two-parters, sometimes designated as such (“Becoming,” part 1, followed by “Becoming,” part 2). As it went along, it became more wedded to season-long stories; the fifth season was the first that didn’t have any two-parters, and that’s because the last few episodes of the season all sort of blended together. The sixth season, with a less unified season-long arc, began and ended with episodes that were designated as two-parters (though I don’t think of the season finale as a genuine two-parter, because the episodes were really just part of a four-episode arc). And the seventh season, which started promisingly and went to pieces, had no two-parters because the last half was all one long, boring undifferentiated story arc.
Now, some shows are episodic but still don’t do two-parters, but that’s because they either don’t want to or the network doesn’t want them to. But if, say, Glee did a two-part episode, we would look at the clock at five minutes of the hour, thinking that something was amiss because the episode’s events didn’t seem to be resolving themselves. We would never look at the clock wondering why a Lost episode hasn’t resolved itself yet.