Should I use a comma before "for"?
When "for" is used as a preposition, it doesn't need a comma:
- He made a cake for her.
- We're away for two weeks.
- It's not for me to complain.
Sometimes "for" can be used as a subordinating conjunction in place of "because". If it starts a dependent clause after the main clause, it shouldn't be preceded by a comma:
- She bought more gloves for she was always losing them.
However, if the independent clause that comes before "for" contains a negative verb, you need a comma:
- He didn't take his umbrella, for the rain had stopped that afternoon.