then, adv. than, conj. (used with adjs. and advs. for comparison or to express diversity or preference)
Of all the commonly confused words I see, this is probably my biggest pet peeve.
Take these two sentences into account:
I would rather eat chocolate THEN spinach.
I would rather eat chocolate THAN spinach.
The first means the speaker would like to have spinach after eating chocolate, while the second means the speaker prefers chocolate to spinach.
As far as my food preferences are concerned, those are two vastly different things.
The easiest way to remember it:
thEn is for Events
thAn is for Analysis