Much of comma use (especially on the ACT) comes down to clauses. A clause is a group of words that contains a subject and a verb. Let’s review.
There are two types of clauses:
Independent clauses
Dependent clauses
An independent clause can stand alone as a sentence. In other words, an independent clause is a complete sentence.
One downside to the digital age is the disappearance of snow days.
This is a complete sentence. It has a subject-verb pair (age-is) and includes all the words that go with that idea.
Dependent clauses still contain a subject and a verb, but they can’t stand alone as a sentence. Usually, this is because a word at the beginning signals that the idea is incomplete and needs to be finished by an independent clause.
Because the pandemic moved us in this direction…
Although we were headed there anyway…
After things settle down…
Each of these is a clause. Each one has a subject-verb pair and the words that go with it (pandemic-moved, we-were, and things-settle, respectively). But none of them expresses a complete thought by itself. Each one needs an independent clause to “complete” the idea, so each is a dependent clause.
Commas matter in two main ways when you join clauses. These rules make up a large portion of the comma questions you’ll see on the ACT.
When a sentence contains one dependent clause and one independent clause, you use a comma only if the dependent clause comes first.
Because the pandemic moved us in this direction, many students have said goodbye to snow days forever.
Here, the dependent clause comes first. Because it comes first, you need a comma between the dependent clause and the independent clause that follows. Notice that what comes after the comma is a complete sentence (an independent clause).
If you rearrange the sentence so the independent clause comes first, you would not use a comma:
Many students have said goodbye to snow days forever because the pandemic moved us in this direction.
There’s no comma between “forever” and “because” because when an independent clause comes first, you don’t use a comma.
Two independent clauses can also involve a comma, but not by themselves (see the chapter on [Comma splices]).
Two independent clauses can be joined by a comma and a coordinating conjunction, better known as the FANBOYS (For, And, Nor, But, Or, Yet, So).
Let’s look at these two independent clauses.
Independent Clause 1: I know I complain too much.
Independent Clause 2: We never get snow days, anyway.
If you join these with a comma + FANBOYS, the sentence looks like this:
I know I complain too much, but we never get snow days.
So, when you want to join two independent clauses, one correct option is comma + FANBOYS.
These questions come up frequently on the ACT, so keep these rules in mind on test day.