The words than and then look and sound very much alike. But, trust me, they are completely different, and I will show you how. These two words are mistaken for one another frequently. If this distinction is difficult for you to grasp right this minute, I'm betting that you'll never forget the difference by the time you've finished reading this post.
Than is a conjunction that is used in comparisons: A conjunction is a word that joins or connects or compares two or more items or ideas or people. Here are some examples of proper use.
Cats are more independent than dogs.
Celery is a more healthy snack than a bag of Oreos.
This seat-belt adjustment is more important than you might think.
Is the Empire State Building taller than the Sears Tower in Chicago?
Will Mariah Carey have more husbands than I will?
Yes, she already has had more husbands than I. (<-- oooo, did you see that pronoun? read on)
Technically, you should use the first-person subject pronoun after than (I, we, he, she), as opposed to the object pronoun (me, us, him, her). There's a good reason for this pronoun choice. The implied, but rarely spoken, continuation of the comparison is some form of the verb: to be (am, are, were, was) or another verb to finish the phrase. So, you would ordinarily finish a comparison sentence with "... more husbands than I (HAVE HAD).) However, many Americans have dropped the completion of this thought in ordinary conversation. Once they decline to finish the thought, some of them think that they sound pretentious if they use the first-person pronoun, so lazy speech has fallen into favor. This pronoun substitution drives grammar geeks such as I (am) absolutely bonkers. But, I digress, let's move on to then.
Then has numerous meanings.
1. At some point in time
I wasn't very old then.
Will you be at work tonight? I'll be in touch with you then.
2. Next, afterward (still refers to time)
I drove to Malibu, and then I had lunch with two movie producers who were wild about my idea.
Pick up after your dog, then wash your hands, and then come to the table for dinner.
3. In addition, also, on top of that (also time, in a looser sense)
Henry informed me that he was terminally ill, and then confided that I would inherit his beach house and baseball cards.
A new car will set you back tens of thousands of dollars, and then there are license fees and insurance, too.
4. In that case, therefore (often with "if") (Technically, this still has a "time" element to it.)
If you want me to support you on this project, then you'll have to convince me that it won't be a money pit.
Child: I'm bored!
Parent: Then I will find something for you to do.
The Easy Way To Remember
Than is used only in comparisons, so if you're contrasting or comparing one thing to another, use than. If your sentence or statement is not a comparison, but refers to time in one form or another, then you have to use then. What could be easier than that?
Here's a sentence to demonstrate the difference. Notice that there are two VERY different meanings, depending on if you use then or than.
I'd rather have a root canal than a blind date. (Oh, do I relate to this! Neither is good, but at least there's a good outcome from a root canal.)
I'd rather have a root canal then a blind date. (What?!? You're some kind of masochist? Two painful activities in the same day?)