Saturday, January 2, 2016

Grammar: Does the word 'so' need a comma in front of it?

So I just learned a neat trick for figuring out whether or not so needs a comma in front of it. Just pop the clause it begins in front of the sentence and, if it’s nonsensical, no comma.

In other words, if the so only meaningfully fits between the two clauses it joins, then that’s a coordinating conjunction. But, if the so clause works at the beginning, predicting something because of something else, for example, it's acting like a subordinating conjunction, so no comma is needed. (Note that the article on Grammar Girl, linked below, never actually says it is a subordinating conjunction. It just says that it acts like one.)

Another thing I noticed was that most of the subordinating-like instances hide an invisible that right after so (or close, such as in so long that), so if you can insert a that in the clause, you probably don’t need the comma. Fun, huh?

So, to recap, if you find a so you're unsure of, move its clause to the beginning or insert a that right after it. If either action makes it sound weird, then so is a coordinating conjunction in that case, and you need a comma.


He wanted to go to the party, so I went with him.
Doesn't make sense if you say: So I went with him, he wanted to go to the party. In this case, so is a coordinating conjunction.

He told me there would be a snack bar at the party so I would go with him.
Here you could state this as, "So I would go with him, he told me there would be a snack bar at the party." That makes sense, so you would treat it like a subordinating conjunction, no comma. It also passes the insert that trick: He told me there would be a snack bar at the party so that I would go with him.

Here are a couple of grammar articles I found helpful with regard to so and other conjunctions. The Grammar Girl one was my primary reference for this post.