When to Use a Comma with So

By Lynn Godson
Jan 10, 2024
5 min read

Have you ever been stuck on whether to use a comma with so? If yes, you’re not alone! So is a tiny word that can lead to major comma confusion – but we’re here to help! In this post, we’ll cover everything you need to know about when to use a comma with so, including handy example sentences. Keep reading to get started!

Coordinating and Subordinating Conjunctions

An understanding of coordinating and subordinating conjunctions is a key aspect of understanding when to use a comma with so.

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 could stand alone as two separate, equally important “sentences” and still make sense; dependent clauses can’t stand alone because they just add extra information about the preceding clause.

Comma Before So

Now we’ve got that out of the way, let’s get back to whether we need a comma before so.

The important grammar tip to remember here is that we only need a comma before so if it’s being used as a coordinating conjunction. If you’re not sure whether so is being used in this way, try swapping it with the word therefore. If the meaning of the sentence is unchanged, then you need a comma before so. For example:

I am going out in the rain, so I should take my umbrella.

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

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

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

In these sentences, you can easily replace so with therefore without changing the meaning of the sentence, so you need to use a comma before so.

However, so can also act as a subordinating conjunction. This is when so is used to present a reason for the first clause, rather than presenting a separate but connected point.

But how can you tell the difference between a coordinating so and a subordinating so?

If, instead of therefore, you can replace the word so with the phrase so that, then so is subordinating and should not be preceded by a comma. Note that the second clause may look independent, but the sentence as a whole describes an action and its purpose or result.

For 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 the hat was bought. That makes it a dependent clause, which makes so a subordinating conjunction here. Therefore, a comma isn’t necessary.

Comma After So

But what if so comes at the beginning of a sentence? Do you need to use a comma after it? It depends on the meaning!

If so is being used in the same way as a coordinating conjunction and leading on directly from the previous sentence, then you don’t need a comma after so. Another way of looking at it is this: can you swap the period for a comma in line with the FANBOYS rule for coordinating conjunctions? If so, then you don’t need a comma after so when it opens the sentence. Here are a few examples:

It’s forecast to rain all day today. So I must remember to take my umbrella.

Nobody wants to read a long, rambling article that doesn’t seem to go anywhere. So it is really important to edit and re-read the content.

We’ve all got a day off work. So we’re all going to the movies.

In each case, you can see the cause-effect relationship between the two sentences. Therefore, there is no need for a comma after so.

If so is not being used as a coordinating conjunction, rather, it’s introducing an entirely distinct clause, then you should include the comma. For example:

Look at this mess you made! So, what do you think we should do about it?

I’m home early from school! So, what’s new?

In these examples, so does not function as a coordinating conjunction. Instead, it’s introducing a new and separate point. Note that this use of so is generally considered informal, so it’s best not to use it in formal or academic writing.

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