In a recent message, a fellow contributor asked about plot and character arcs. Specifically, what is a plot arc? What is a character arc? How do these things work?
In TV, there are two primary modes of storytelling: episodic and serial. "Episodic" is where each episode tells a complete story and the characters and situations rarely change. Think "Law and Order" or "CSI" or "Star Trek". Characters are static, and very often, character histories change as the story demands.
"Serial" shows, on the other hand, may have relatively complete stories in each epsiode, but the overall show involves events that have consquences for the characters and their development. "Babylon 5" is a classic example, as well as "Buffy", "Angel", and "Lost". These shows tend to delve into characters and their decisions, so the characters tend to change over time as events push them into new territory.
A "plot arc" is a sequence of events, typically spanning a season. Usually it involves three phases: an introductory phase, where conflicts and situations are established; a complication phase, where the conflicts erupt and events spiral out of control; and a resolution phase, where the conflicts are resolved, usually setting the stage for the next plot arc.
For example: a typical season of "Buffy" would begin with about 6-7 episodes that would begin introducing the next big threat and the character conflicts in play since the previous season. There would be a major revelation, followed by 6-7 episodes that would seriously complicate everyone's lives and force them to uncover the threat and anything related to it. That usually would lead into another major revelation, and then 6-7 episodes would be spent on defeating the threat that had emerged, usually with major consequences to the characters.
Most "serial" shows with distinct season arcs are patterned in this way over the course of 22 episodes. Initial setup, 6-7 episodes of introduction, big event, 6-7 episodes of fallout and complication, big event, 6-7 episodes leading into the big resolution.
It's not always event-driven; sometimes it can be thematic, where a major question is raised in the season premiere and the question is answered by the end of the season. Usually this happens when the season is dominated by "character arcs". This is where certain characters change in response to the events in the season arc, usually in some major and undeniable way.
A strong "serial" series will have several plot and character arcs all going at the same time (again, think "Babylon 5" or "Lost"). A weak "serial" series might have a plot arc with weak character arcs (or none at all).
Some shows (like "X-Files", for example) try to meld the "episodic" and "serial" types into something of a hybrid. This is where most episodes are "episodic" in nature, but there are still big events where they would usually fall in the schedule for a "serial" series. It just so happens that this is usually coincidental with the traditional "sweeps" period for TV ratings!
Hopefully this clears up what I mean when I talk about "plot arcs" and "character arcs".