Commas before "Then"

A comma is sometimes required before the word "then."

The rule is fairly simple: "then" can mean "at the appointed time" or "in that case," and if you're talking about the latter, then you usually need a comma before the word. If you're talking about the former, you almost never need the comma. The exception to this is if you're using "then" as a conjunctive adverb to connect parts of a sentence. In that case, you need a comma before it.

For example:

We went to the beach then. ("Then" is the time that we went to the beach, no comma is needed.)

It's decided, then. ("Then" is used to mean "in that case," so a comma is needed.)

He opened the door, then stepped inside. ("Then" is being used as a conjunctive adverb, so you need a comma before it. Note, however, that if you use a real conjunction with the adverb you don't need the comma. E.g. He opened the door and then stepped inside.)

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