When to Use a Comma with So

This post will explain when to use a comma with so. So is a tiny word that can lead to major comma confusion, so read on for our straightforward explanation. We’ll also cover coordinating and subordinating conjunctions because an understanding of them is important for this topic. And we like to give you that extra bit of help. We’re nice like that!

Coordinating and Subordinating Conjunctions

Conjunctions are words that join clauses, phrases and other words together. They have a mnemonic that makes remembering some of them easier: FANBOYS (for, and, nor, but, or, yet, and so).

The nature of a conjunction depends on the nature of the clauses that it joins together. If a conjunction joins independent clauses, it’s called a coordinating conjunction. If it joins an independent and a dependent clause, then it’s a subordinating conjunction. Independent clauses can stand alone and still make sense; dependent clauses can’t because they just add extra information.

Now we’ve got that out of the way, let’s get back to our little friend, so.

The important grammar tip to remember here is that we do not use a comma with so when it is a subordinating conjunction. Just ask yourself whether the clause after so can stand alone. If it can’t, don’t use a comma with so.

Here’s an example:

I bought a new hat so I had one to match my new dress.

The independent clause here is “I bought a new hat”. It can stand alone and still make sense. The clause after so just adds more information about why I bought a new hat. That makes it a dependent clause, which, in turn, makes so a subordinating conjunction. Therefore, we don’t use a comma.

An easy way to check is this: if you can put so that instead of so, and the sentence still makes sense, so is a subordinating conjunction, and we don’t use a comma.

I bought a new hat so that I had one to match my new dress.

Our example still makes sense.

Comma before So

So much for so as a subordinating conjunction. But what do we do if so is a coordinating conjunction (i.e., one that joins independent clauses)?

Easy answer: put a comma before so.

Here’s an example of so as a coordinating conjunction joining two independent (equally important, stand alone) clauses.

My friend was ill, so I went to see him.

Both of these clauses can stand alone and still make sense, and they are equally important. That makes them independent clauses, and that makes so a coordinating conjunction. Hence, we use a comma before so here.

The same principle applies in these examples:

I’m a keen supporter of my local baseball team, so I always go to their games.

John’s garden was looking untidy, so he mowed the lawn.

She needed some fresh air, so she went for a walk.

A quick tip here is: if so can be replaced by therefore and the sentence still makes the same sense, so is a coordinating conjunction, and we use a comma before it.

Comma after So

Up to now, we’ve looked at examples where so joins two clauses, but so can also start a sentence. So, we should look at what to do then. As you can see from the previous sentence, when so is at the beginning of a sentence, we use a comma after it.

Take a look at a couple more examples of so at the start of a sentence.

So, how shall we fix this mess?

So, listen carefully!

A comma also goes after so when so is used to introduce a parenthetical dependent clause. A parenthetical dependent clause is inserted into a sentence to give more information (our previous examples of dependent clauses just followed straight on after their independent clauses). Take a look at these examples.

We’re going to the shopping mall this afternoon, so, if you want us to buy you something, you need to tell us before then.

It looks like it might rain later, so, if you’re going out, you should take an umbrella.

So, What Next?

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