My friend and I have a saying about science fiction: Dead is not dead.

I wished I had remembered that before I got all tweaked about Derek Reese getting killed off on Terminator: The Sarah Connor Chronicles. Guess who showed up alive and well in last night’s season finale, thanks to a time-traveling John Connor?

Uncle Derek! Yeah!

Not all science fiction abides by the “Dead is not dead” concept, but a lot of it does. Sometimes it’s through time travel (as was the case with Terminator—travel to a time where Derek hadn’t been shot and, voila!, there he is). Sometimes it’s through technology (cloning, Replicator technology, and Cylon technology kept dead characters around on both Atlantis and Battlestar Galactica). Sometimes it’s through powers and forces beyond our human comprehension (I lost track of how many times Daniel Jackson came back from the other side on Stargate: SG-1). And sometimes you don’t know exactly why the dead aren’t dead, but you don’t care—you’re just happy they’re not dead (Lost!).