With examples from Stargate SG-1, Stargate Atlantis, and The X-Files.
How many times have you see something like the following in a fic: "Scully was more skeptical then Mulder?" The problem with the sentence is that the word "then" is used incorrectly. What the author means is "than."
"Than" and "then" are two of the most commonly misused words in fic, and using them inappropriately can jerk a reader right out of the story. So how can you remember which word to use in which situation?
Besides being only one letter apart, "than" and "then" can also sound very similar when said aloud. But the two words have very different meanings.
"Than" is a conjunction that is mainly used to make a comparison between two nouns that are somehow unequal or different from each other:
Zelenka didn't argue with Ronon's decision, because Ronon was much bigger than him.
In this example "than" is used to note the relative difference in size between two nouns (Zelenka and Ronon).
This usage of "than" also applies to making statements of preference:
Rodney buried his face in his hands. At this point, he would rather face a starving Wraith than spend another second listening to these idiots.
"Then" is mostly used as an adverb (though in some cases it can be an adjective or a noun). It always refers to time.
"Then" can indicate the next thing in a series of events:
Dana Scully's mornings were always the same. She would wake up, take a shower, and then grab a bagel before bracing herself for whatever Mulder would throw at her that day.
"Then" can indicate some point in the past:
Jack O'Neill, wincing a little, tried not to rest any weight on his bad knee. It was times like these when he realized he wasn't thirty anymore. Field missions had been so much easier back then.
"Then" can also indicate the logical conclusion to something, otherwise known as the "if...then" statement:
If Carter could hold off the Goa'uld long enough, then Daniel would be able to dial the gate.
So returning to our original problem sentence: "Scully was more skeptical then Mulder," you can see now how it doesn't make sense, because it is comparing two things and has nothing to do with time. The correct sentence would be: "Scully was more skeptical than Mulder."
Use "than" when making a comparison, and "then" when referring to an event in time. Remember this, and it'll be easy to remember when to use which.
Ronon was so hungry he ate more than the rest of his teammates combined, and then he went back for seconds.