The core distinction
"Then" and "than" are separated by a single letter, but they serve entirely different purposes. "Then" is about time or sequence: it tells you what happens next. "Than" is about comparison: it tells you how two things measure against each other.
This confusion is one of the most common errors in English writing. It appears in professional emails, published articles, and even edited books. The good news is that the rule is simple once you internalize it.
When to use "then"
"Then" functions as an adverb that relates to time. It can mean "at that point," "next in order," or "in that case." Whenever your sentence involves a sequence of events or a conditional outcome, "then" is the correct choice.
- We finished the report, then submitted it to the client.
- If the budget is approved, then we can begin hiring.
- Back then, remote work was considered unusual.
- First add the flour, then stir in the eggs.
When to use "than"
"Than" is a conjunction (or sometimes a preposition) used exclusively for comparisons. If you are measuring one thing against another, bigger, smaller, faster, more expensive, you need "than."
- This approach is more efficient than the previous one.
- She has more experience than anyone else on the team.
- The presentation took longer than expected.
- I would rather rewrite the draft than submit it unfinished.
A quick editing test
If you can substitute "next" or "afterward" and the sentence still works, use "then." If you can substitute "compared to" or "relative to," use "than." This swap test catches nearly every case.
One other tip: read your sentence aloud. "Then" and "than" are often pronounced slightly differently in careful speech, and your ear may catch what your eye misses.