Commas with Which, That, and So

Commas show up on the ACT English test more than any other punctuation mark.

Using a comma correctly means knowing a few situation-based rules. Because commas have so many rules, the test makers use them often.

Besides separating or connecting clauses, commas also follow specific patterns depending on the words that come right before or after them.

Here’s the key idea:

Use a comma before “which,” don’t use a comma before “that,” and sometimes use a comma before “so” (but not when it means “so that”). If that feels confusing right now, the examples below will make it clear.

These rules can be confusing because they’re easy to mix up, and they can seem like they overlap.

This lesson breaks them down so you know exactly what to do on test day.

Using commas with “which”

“Which” usually begins what’s called a nonrestrictive phrase, which (see what we did there?) is just a phrase that adds extra information that isn’t essential to the sentence.

Because a nonrestrictive phrase is an interruption, you typically put a comma before “which.” If the phrase ends before the end of the sentence, you also use a comma to close it.

Example

His denial didn’t tell the whole truth, which was that he knew who had done it.

I couldn’t believe what the doctor said, which was that there was no longer any trace of cancer.

Not using commas with “that”

“That” usually begins a restrictive phrase, meaning the information is essential to the sentence.

Because the phrase is essential, you don’t put a comma before it.

Example

The man who was sitting next to me probably had COVID.

Notice what happens if you remove the phrase “who was sitting next to me.” It becomes unclear which man the sentence is talking about.

In other words, you need “who was sitting next to me” for the sentence to communicate its intended meaning. That makes the phrase restrictive, so you don’t use commas.

Sometimes using commas with “so”

The word “so” is tricky because it can work in two different ways.

Sometimes, it’s a coordinating conjunction (a FANBOYS word) that links two independent clauses (see the chapter FANBOYS and Joining Clauses).

Example

I learned to speak Japanese, so now I don’t use subtitles when watching anime.

Here, you need a comma before “so” because it’s joining two independent clauses.

• Independent Clause 1: I learned to speak Japanese
• Independent Clause 2: now I don’t use subtitles when I watch anime

To join the two independent clauses, you place a comma plus “so” between them.

Other times, “so” comes right before “that.” When this happens, you don’t need a comma.

Example

I dropped by the store on the way home so that I could grab some milk and bread before the snow.

Here, “so that” functions as a subordinating conjunction, which means you would NOT put a comma before it.

These rules can feel like a lot at first, but on the ACT you mainly need to remember this set of patterns: