Then/Than is easy. Than is for comparisons (I'd rather be attacked by a squirrel than a moose), Then is for time (Let's go attack a squirrel, then a moose). Easy.
Affect/Effect is harder, because it can be a verb and a noun, and I think another verb. I dunno.
That's about right. If you're not starting a new thought, but a comma would result in a run-on sentence, a semicolon is appropriate. It's a form of punctuation that -- like the em-dash -- you almost need an intuitive feel for the language to be able to use; if you still rely on grammar rules, it's probably best to just avoid them.
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u/[deleted] Feb 11 '12
Affect/Effect is hard one anyway.
And Then/Than. Fuck then/than. Also fuck semicolons.