Poor grammar, poor grammar everywhere!

I don't have time for my Nazi costume, Woody - so I'll make this quick. You use "an" when it precedes a word that starts with a vowel sound, like "an hour" or "a cowboy". The word "than" is used for comparisons, whereas "then" indicates a specific point in time. For example: I've worn a hat for an hour, then I wore one bigger than this one. Next lesson: "less than" vs. "fewer than" and why grocery store express lanes are usually wrong!