The joining-comma rule mentions that two complete clauses may be joined with a comma if the clauses are short or the comma is followed by a coordinating conjunction. So, I suppose that I should write

When I arrived home I fell asleep, for I was exhausted.

When I arrived home I fell asleep because I was exhausted.

However, what puzzles me is that "for" does have a causal (subordinate) role. Here, the logic of the language escapes me. Please, can someone clarify this point?

  • Remember: life is short, break the rules -- they were made to be broken. [James Dean, 1931-55]
    – Andrew Leach
    Feb 11, 2013 at 23:22
  • 2
    Thanks Andrew, but I already break so many rules by ignorance that it would be nice to learn a bit more before breaking this one.
    – The Frog
    Feb 11, 2013 at 23:38
  • Related.
    – tchrist
    Nov 24, 2022 at 20:37

2 Answers 2


Well, a causal relationship can exist between two completely separate sentences, even with a sentence between them:

Alice was sent to jail. I just heard it on the news. She'd been embezzling from Bob.

So while we could join the first and third sentences as clauses in a single one, using for or because:

Alice was sent to jail, for she'd been embezzling from Bob.

It remains, that the two clauses are independent clauses.

  • Are you saying that punctuating as follows is correct? "When I arrived home I fell asleep, because I was exhausted."
    – The Frog
    Feb 12, 2013 at 0:47
  • Are you saying that you could write "Alice was sent to jail, because she'd been embezzling from Bob."?
    – The Frog
    Feb 12, 2013 at 0:54
  • 1
    @TheFrog I certainly wouldn't worry about a comma in either of those sentences; in fact I'd positively prefer it in the "fell asleep" one. And in the "for" sentence in the question, which is the reason for my (admittedly flippant) quote from James Dean: sometimes, a "rule" needs to be broken.
    – Andrew Leach
    Feb 12, 2013 at 0:56
  • I agree with @AndrewLeach I'd consider the comma optional in both. With, it slightly emphasises the two ideas' separate truth. Without it it slightly emphasises the causality. Both though state both the causality as well as each statement, so there's no significant change in meaning. With for there's a good argument for strongly favouring a comma before the for simply because it helps distinguish such uses from many of the other uses for has. Even there though, it can still be left out, especially with very short clauses either side.
    – Jon Hanna
    Feb 12, 2013 at 1:04
  • Thank you very much for your answers. They are very helpful to me. As you may have guessed I am not a native speaker.
    – The Frog
    Feb 12, 2013 at 8:34

Essentially, "for" does offer a reason and binds the two independent clauses together. Because the sentence is so short, a comma here would be optional. In longer sentences, it would be necessary. But I would keep the comma for clarity. And the FANBOYS usually come with the comma and two I.C.s.

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