1. "Then" as an Adverb of Time:
* No comma: If "then" simply indicates a sequence of events, you don't need a comma.
* Example: *I finished my work, then I went to the store.*
2. "Then" Introducing a Dependent Clause:
* Yes, use a comma: If "then" introduces a dependent clause that needs a comma to separate it from the independent clause, you should use it.
* Example: *I went to the store, then I realized I had left my wallet at home.* (The clause "then I realized I had left my wallet at home" depends on the first clause for its meaning.)
3. "Then" as a Conjunction:
* Generally no comma: When "then" acts as a conjunction (like "and" or "but"), you don't usually need a comma.
* Example: *I finished my work and then went to the store.*
4. "Then" for Emphasis:
* Yes, use a comma: If "then" is used to emphasize a particular point, you may want to use a comma.
* Example: *I went to the store, then, I found a great deal on shoes.*
In short, consider the function of "then" in your sentence to determine whether a comma is needed. If in doubt, you can often rephrase your sentence to avoid the comma entirely.