Should there be a comma before "or" in the sentence below? I think keeping the comma would be a comma splice, but I am not completely sure.

It is a disorder in which a missing or garbled sequence of DNA leaves the body unable to make a particular protein, or causes it to be made in an abnormal form.

  • 3
    I think by definition this is nothing to do with comma splices, since they involve joining two independent clauses with nothing more than a comma (yours has the conjunction or, and what follows isn't an independent clause anyway). For legibility, if nothing else, I think you should keep your comma. Aug 24, 2015 at 15:56
  • 1
    As @FumbleFingers says, definitely not a comma splice. Commas are relatively mandatory when joining complete independent clauses with explicit subjects, but not when the second clause does not explicitly state its subject (taking it from the first clause instead) as is the case here. But ‘not mandatory’ doesn’t mean ‘wrong’—it just means you don’t have to put a comma there. The longer and more complex the clauses get, the more sense it often makes to have a comma there; in your case here, it works just fine. Aug 24, 2015 at 16:11
  • @Janus: In this particular case it's unfortunate that we (us here on ELU, who can't see the preceding context) are already "left hanging" because we don't know exactly what the first it refers to. I'm sure the second it is intended to refer back to a particular protein, but strict logic, semantics, and syntax can't rule out the possibility of it referring to the body. Which might net down to the same thing anyway, since a body that makes abnormal forms of proteins is likely to be "abnormally formed" itself. Aug 24, 2015 at 16:23

2 Answers 2


You should use a comma to separate independent clauses joined by a conjunction in a single sentence. That is, if each clause has a subject and a verb and can stand on its own as a sentence, you use a comma. Here's an example:

Baseball is not Jane's favorite sport, but she does enjoy a good game on occasion.

A comma should not be used, though, if you're using a conjunction to join a phrase to a clause in such a way that the phrase is a secondary action performed by the subject and could not stand as a sentence on its own. Here's an example:

Andy loves baseball and plays whenever he can.

Commas should be used, though, when you join two or more phrases to a clause. This is because you should treat the joined phrases similar to a list. To see what I mean, consider this simple sentence: "I had salad, pasta, and bread sticks for dinner last night." You need to use commas to separate lists of phrases the same way you do lists of other items. Here's an example:

Lucy picked up her bat, stepped up to the plate, and prepared for the first pitch.

You can use this information to answer your question. I write answers like this because the information is more generally useful to a larger audience than just giving the plain answer. Also, if you can apply this information to figure out the answer on your own, you'll remember it better. Feel free to comment if you're uncertain and want to confirm.


If the sentence in question had simply said

This disorder prevents the body from making a particular protein, or causes it to produce abnormal proteins.

you might argue that the comma is superfluous because the sentence's parallel structure is immediately evident to readers and amounts to

This disorder (1) prevents the body from making a particular protein or (2) causes it to produce abnormal proteins.

But as Janus Bahs Jacquet observes in a comment above, the fact that a comma isn't mandatory in a parallel construction like this one doesn't mean that including one is wrong. I don't deny that a comma may sometimes act as a needless (though very minor) impediment to brisk reading, as here:

My father eats pretzels, and drinks beer.

but I don't think that the comma in my shortened version of your original sentence has that hindering effect, and I certainly don't think that the comma in the original sentence does. If anything, it usefully marks where the second branch of the parallel structure begins.

None of this discussion is related to comma splices—because, as FumbleFingers observes in a comment above, the comma in your original sentence doesn't create a comma splice. If it had done so, you'd have been able to confirm that fact by setting up the clause after the comma as a separate sentence and seeing that it was complete. Since

Causes it to be made in an abnormal form.

doesn't work as a complete sentence, there is no comma-splice issue here.

Not the answer you're looking for? Browse other questions tagged or ask your own question.